The Fundamental Problem in Thread Gaging and Thread Gage ... · Thread Set Plugs and Thread Ring...

NCSL International Workshop & Symposium | Measurements of Tomorrow August 27-30, 2018 | Portland, Oregon

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The Fundamental Problem in Thread Gaging and Thread Gage Measurement

Speaker/Author: Travis Fletcher

Quality Engineer / Process Engineer

JJ Calibrations, Operations Manager

Portland, OR 97267-2105

503-786-3005

[email protected]

Since the introduction of threads and thread specifications measurement practices have made

assumptions based of formulas and calculations. While this has allowed for what has been deemed as

adequate measurement of threaded parts and gages technological advances have brought to light some

fundamental issues.

For the sake of this evaluation, we will be focusing only on 60° Unified Screw threads. Specifications

for these types of screw thread parts can be found in ANSI /ASME B1.1 (Unified Screw Threads) and

ANSI / ASME B1.2 (Gages and Gaging for Unified Inch Screw Thread Series).

To ensure that threaded products produced meet specifications, Go / NoGo thread plugs and thread

rings are typically used. In theory, this is pretty simple; The Go Gage must pass the threaded section of

the part and the NoGo gage must NOT pass.

Inspection of Internally Threaded Parts

Inspection of internal threads has traditionally been with the use of thread plug gages. Parameters for

inspection of these types of internal threads are typically simplified to two main requirements; Pitch

Diameter (PD) and Minor Diameter. The Go Gage is designed to encompass the low end of the

specification for the PD (with + tolerance applied) and the major diameter to account for the nominal

size of the thread size designation (with + tolerance applied). The NoGo Gage is designed to

encompass the high end of the specification for the PD (with - tolerance applied) and the major

diameter to account for the nominal size of the thread size designation (with - tolerance applied). Pretty

simple, right? So, how are these gages that are manufactured to inspect threaded parts being

manufactured being inspected? Please, read on...

Inspection of Externally Threaded Parts

Inspection of external threads has traditional been with the use of thread ring gages. Again, parameters

for inspection of these types of internal threads are typically simplified to two main requirements; Pitch

Diameter (PD) and Major Diameter. The Go Gage is designed to encompass the high end of the

specification for the PD (with - tolerance applied) and the major diameter to account for the nominal

size of the thread size designation (with - tolerance applied). The NoGo Gage is designed to encompass

the low end of the specification for the PD (with + tolerance applied) and the major diameter to account

for the nominal size of the thread size designation (with + tolerance applied). So, again, how are these

gages that are manufactured to inspect threaded parts being manufactured being inspected? Please read

further on for explanations, but first we need to also discuss other facets of the inspection of externally


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threaded parts that should mentioned. On External Threads, the PD's and major diameters are typically

also verified using other methods as well. I have come to the conclusion that while this is a great

practice the only reason this is done on external threads and and not on internal threads is because it

CAN be done without having to destroy a sample part to obtain measurements by sectioning it. Major

Diameters are typically measured using an OD micrometer. PD's are often measured using a thread

pitch micrometer, a Johnson Gage roll comparator, or with and OD micrometer, using the 3-wire

method. For the sake of this evaluation, we will only be focusing on measurements with an OD

Micrometer, with adequate resolution / accuracy for these tight tolerances; I.E. and indicating

micrometer or “supermic.” (Feel free to contact me if you want additional information on the other

methods mentioned).

Measuring of Pitch Diameters using a Supermic and the 3-Wire Method

The 3-Wire Method can be used to measure externally threaded parts, thread plug gages (used for

inspecting internally threaded parts), and thread set plugs (used for inspecting and setting thread ring

gages that are in turn used to inspect externally threaded parts). Before we get much further into

measuring using the 3-Wire Method, we first need to understand what the Pitch Diameter (PD) is.

So, what is a pitch diameter of a screw thread? The best definition that I have run across is as follows:

The diameter of a theoretical cylinder that passes through the threads in such a way that the distance

between the theoretic sharp corner of thread crests and the theoretic sharp corner of the thread roots is

equal. So, how do we measure the theoretic points of features that create a theoretical cylinder? To put

it simply, the only way is to do it “theoretically”, making some assumptions and performing

calculations using mathematical formulas for constants. Huh? Basically, you cannot measure to and

from surfaces that do not physically exist. So, how are measurements actually obtained? PD

measurements can be performed by using the 3-Wire Method to simulate measuring the actual PD. For

example, on a 1/4-20 UNC-2B thread plug gage, a wire size is determined using the following formula

(applies to all 60° Unified Inch Screw Threads):

.57735 / Threads Per Inch (TPI) = Best Wire Size

.505182 / TPI = Min Wire Size

1.010363 / TPI = Max Wire Size

With a TPI of 20, the Best Wire Size is calculated as .0288675 (rounded up to .028868)

With a TPI of 20, the Min Wire Size is calculated as .0252591 (rounded down to .025259)

With a TPI of 20, the Max Wire Size is calculated as .05051815 (rounded down to .050518)

If these exact wire sizes are not available, as long as the 3 available wires are the same size (within

specifications for thread measuring wires) and within the min / max wire sizes allowed, we can still use

the wires to obtain measurement results by applying the following formula:

C=3W- (.866025p)

Where

C = Constant to be used in 3-wire method

W = Mean (average) of thread wires

p = pitch

Given our example of 1/4-20 threads, let’s say only three .0300” wires were available for use. We can


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use these wires by calculating the following:

(Thread wires are theoretically the same exact size for this example)

TPI = 20 or .050 pitch (1 inch divided by 20 Threads Per Inch)

p = .050

W = .0300”

3x.0300 = .09

.866025 x .05 = .04330125

.09-.04330125 = .04669875 Rounded to 6 decimals = .046699 (Constant)

The constant is the numerical value that is subtracted from the measurement over the wires placed in

threads of the unit under test (the part or gage to be measured).

Thread wires should be placed in the threads of the unit under test as shown below:

Measurements over wires obtained should have the constant subtracted from the measurement result to

obtain the calculated Pitch Diameter. Measurement Over Wires (M.O.W.) - Constant ( C ) = PD

Unfortunately, and as previously mentioned, this is a theoretical calculation of the pitch diameter using

mathematical formulas and may not capture the actual pitch diameter. What this method captures is

what is known as the “simple pitch diameter.” So, how do we measure the actual effective Pitch

Diameter? Up until only the past couple of years, there really wasn't a way to legitimately measure the

actual Pitch Diameter. Now, with improvements in Technology, there is by scanning the profile of the

threads using a contact scanning measurement device.


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Why Contact Profile Scanning?

Contact profile scanning allows for actual contact measurement of the critical features of the thread that

constitute the true effective pitch diameter. This method is already widely practiced in most parts of

Asia. In Europe, the method has become the standard from which most thread measurements are

derived (ref Euramet cg-10). This method removes several of the variables that occur during the 3-wire

method for pitch diameter measurement while also capturing the entire profile of the thread instead of

just a small section that the wires come into contact with along the thread flanks. Additionally, this

method removes the potential for tolerance stack-up by relying on the accuracy of the scanning device

and probe rather than the accuracy of each of the 3 wires and the super micrometer while

simultaneously reducing the variation of measurement result by different inspectors.

Thread Set Plugs and Thread Ring Gages

As previously mentioned, inspection of external threads has traditionally been with the use of thread

ring gages. To ensure that threaded products produced meet specifications, Go / NoGo thread rings are

typically used. The Go Gage must pass over the threaded section of the part and the NoGo gage must

NOT pass. So, how are these thread ring gages that are being manufactured being inspected to ensure

that they meet specifications? Up until recent technological advances, thread set plugs have been used

for this purpose. Thread Ring Gages are threaded onto a thread set plug to ensure proper feel on both

the truncated portion and full form portion of the thread set plug. Proper feel has been defined as

“Some Drag” or “Slight Drag.” What could be clearer than that, right? Being more of a data-driven

person, this is extremely subjective in my opinion and I have seen countless man-hours spent on this

discussion. What may feel like “some drag” or “slight drag” to Inspector A may be drastically different

from what Inspector B feels as the correct fit. This being said, there is a little more to it than just “some

/ slight drag.” In addition to the thread ring gage being threaded onto both the truncated and full form

of the thread set plug with slight drag, there should also be no difference in feel between the truncated

and full form sections. There should also be no “wobble” detected while threading the ring onto the

thread set plug. There should also be no difference in feel or any wobble detected when the gage is

flipped over and ran onto the set plug from the opposite side. Again, these requirements are subjective

and open to interpretation and may be the subject of lengthy discussions between operators, QA

personnel, calibration technicians, etc. So, what does it mean if the drag is not tight enough? What does

it mean if the drag is too tight? What does it mean if there is a difference in feel between the truncated

and full form sections of the thread set plug? What does it mean if there is wobble? What does it mean


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if one side of the gage feels correct, but when it is flipped over and ran onto the set plug from the

opposite side it feels different, has wobble, is too loose or too tight? Let me explain:

On fixed (non-adjustable) thread ring gages, the ring should be replaced if:

Drag is excessive and the ring does not turn adequately (without significant force) on either the

truncated section or full form section of the thread set plug.

There is not enough drag on either the truncated section or full form section of the thread set

plug and the ring is “free-spinning.”

The ring gage exhibits wobble or excessive slop when run onto either the truncated or full form

section of the thread set plug.

One side of the ring threads onto the thread set plug, but when turned over and threaded on

from the opposite direction, there is excessive drag, not enough drag (free-spinning), or wobble.

On adjustable thread ring gages:

If drag is excessive and the ring does not turn adequately (without significant force) on the

truncated section of the thread set plug, it will need to be adjusted (loosened) to fit the truncated

portion of the thread set plug.

If there is not enough drag on the truncated section of the the thread set plug and the ring is

“free-spinning”, it will need to be adjusted (tightened) to fit the truncated portion of the thread

set plug appropriately.

If drag is excessive and the ring does not turn adequately (without significant force) on the full

form section of the thread set plug, but it threads on to the truncated section correctly, the gage

may be able to be adjusted, however, this is somewhat difficult. Consider replacing the gage, as

the flanks may be worn.

If there is not enough drag on the full form section of the the thread set plug and the ring is

“free-spinning”, but threads on to the truncated section correctly, the gage may be able to be

adjusted, however, this is somewhat difficult. Consider replacing the gage, as the flanks may be

worn.

Potential for Tolerance Stack-up & TAR with the 3-Wire Method

Now that we understand the interaction between the thread set plug and the thread ring gage, lets re-

visit the 3-wire method of inspection for PD's on thread set plugs. Going back to our example of 1/4-20

threads, the tolerances for thread measuring wires, thread set plugs, and thread ring gages are shown

below:

Thread Measuring Wires:

±.000020” of best wire size

±.000005” of specified wire size

±.000005” of each 3 wires to each other

±.000010” roundness

1/4-20 UNC-2A thread set plug (Go member used for example)

.2164” +0 / -.0002” Pitch Diameter

.2489” ±.0004” Major Full Form Diameter

.2399” +0 / -.0004” Major Truncated Diameter


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1/4-20 UNC-2A thread ring (Go member used for example)

.2164” +0 / -.0003” Pitch Diameter

.1948” +0 / -.0005” Minor Diameter

For arguments sake, lets assume conditions where ALL measurements were at the absolute minimum to

still be considered acceptable;

Thread measuring wire:

Best Wire Size .028868 -.000020 = .028848

Specified wire size .028848 -.000005 = .028843

High wires = .028843

Low wire = .028843-.00005 = .028838

Out of round condition min = .028837

Out of round max = .028844

In actuality, the wires specified as .028843 can measure as much as .028844 and as low as .028837

depending on where the measurements are taken. How does this effect measurements on the thread set

plug? A .000007” difference in thread wires wouldn't effect a measurement on a thread set plug, right?

Not exactly, if not accounted for correctly, with a new constant calculated, a .000007” difference in

thread wires could change the constant by .000021”. With the constant being the number that is

subtracted from the measurement over wires (M.O.W.) to obtain the calculated, simple pitch diameter,

this could drastically impact measurement results. With this value in addition to typical accuracy of a

super micrometer of ±.000020”, measurements of calculated pitch diameter could be off by as much as

.000041”, or over 20% of the allowable tolerance of the thread set plug. While this is acceptable as it

meets a 4:1 Test Accuracy Ratio (T.A.R.), consider the following;

At a measured PD of .2164” (max PD for 1/4-20 UNC-2A thread set plug) the unit under test could

actually measure .216441”.

At a measured PD of .2162” (min PD for 1/4-20 UNC-2A thread set plug) the unit under test could

actually measure .216159”.

Set Plugs and Thread Ring Gage Tolerances Compared to Manufactured Nut / Bolt

Specifications

Going back to our example of 1/4-20 threads, the tolerance for thread set plugs, and thread ring gages

are shown below:

1/4-20 UNC-2A thread set plug (Go member used for example)

.2164” +0 / -.0002” Pitch Diameter

.2489” ±.0004” Major Full Form Diameter

.2399” +0 / -.0004” Major Truncated Diameter

1/4-20 UNC-2A thread ring (Go member used for example)

.2164” +0 / -.0003” Pitch Diameter

.1948” +0 / -.0005” Minor Diameter

Do the gages manufactured actually meet these specifications?


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In reviewing thread ring gages specifications, once again using our example of 1/4-20 UNC-2A, the

pitch diameter requirements for the GO ring is listed as .2164” +0 /-.0003”, or .2164”-.2161”. The

correlating thread set plug GO member requirements for pitch diameter is listed as .2164” +0/-.0002”,

or .2164-.2162”.

Generally speaking, NO, the adjustable thread ring gages manufactured to meet these specifications do

NOT meet the defined dimensional tolerance. Here is my theory as to why;

Let’s go back to our definition of the pitch diameter: The diameter of a theoretical cylinder that passes

through the threads in such a way that the distance between the theoretic sharp corner of thread crests

and the theoretic sharp corner of the thread roots is equal.

If the diameter of a shaft made of steel and the diameter of a hole machined out of steel are the same

size, will the shaft enter the hole with “slight drag”? No, the shaft would have to be slightly smaller to

enter the hole or use significant force to be driven into the hole. Even though the the pitch diameter is a

theoretical cylinder, it is still based off of the flank angles of the thread. Knowing that thread ring gages

and thread set plugs are manufactured from steel (sometimes chrome), it is not possible for a steel shaft

(I.E. the set plug) to enter the hole machined from steel (I.E. the thread ring gage) without significant

force being applied. In reference to ANSI B4.1 for Standard Tolerance Limits and Fits, there are 3 main

classes of fit: Running or Sliding Fits [RC], Locational Fits [LC, LT, LN], and Force or Shrink Fits

[FN]. The Locational Fit class can be broken down into 3 sub-classes; Clearance Locational Fit [LC],

Transition Locational Fits [LT], and Interference Locational Fits [LN]. While this specification applies

to non-threaded cylindrical features, I believe a little can be learned from this standard in regards to

the fit of a thread ring gage onto a thread set plug.

Revisiting our use of the thread set plug and proper testing of the thread ring gage:

Thread Ring Gages are threaded onto a thread set plug to ensure proper feel on both the truncated

portion and full form portion of the thread set plug. Proper feel has been defined as “Some Drag” or

“Slight Drag.”

The “Slight Drag” description would best fit the Running or Sliding Fit classification of RC2 in ANSI

B4.1; Intended for accurate location made to move and turn easily but not freely. I believe this can

further be substantiated by matching the tolerance band of the PD for the 1/4-20 UNC-2A thread ring

gage of .2164”-.2161” to hole requirements for this class of .2164-.2161” when the nominal size is

specified at .2161”. However, when compared to the shaft requirement of .21595-.21575” for this class

of fit compared to the set plug requirements of the 1/4-20 UNC-2A thread set plug of .2164-.2162” we

see a problem. ANSI B4.1 knows that for this class of fit, the shaft (set plug in example) must be

slightly smaller than the hole (ring gage in example). To get even remotely close to the matching the

dimensional requirements of the 1/4-20 UNC-2A thread ring gage and thread set plug, we have to look

not one or two classes of fit beyond RC2, but rather 9 classes to class LN 1 (Locational Interference

fit), with a hole requirement of .2164-.2161” compared to a shaft requirement of .2166-.2164”.

“Slight Drag” of the thread ring gage cannot be achieved by threading it onto the thread set plug with

the amount of force required if both the thread set plug and the thread ring gage met the dimensional

limits of the specifications.

It is obvious that the writers of thread specifications know this, as when we review the specifications


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for externally threaded parts / screws / bolts and internally threaded parts / nuts we see that the Pitch

Diameters of the mating parts do NOT overlap:

Pitch Diameter for Externally threaded parts / screws / bolts for 1/4-20 UNC-2A thread requirement is:

.2164-.2127”

Pitch Diameter for Internally threaded parts / nuts for 1/4-20 UNC-2B thread requirement is:

.2224-.2175”

In other words, the theoretical cylinder of the pitch diameter of the shaft (screw / bolt) CANNOT be the

same size as the pitch diameter of the hole (nut) to function correctly. The shaft (screw / bolt) must be

at least .0011” smaller than the hole (nut). This of course, would be a looser class of fit, though, as we

don't want our threaded parts having “slight drag” as we want our rings to thread onto our set plugs.

This is why min / max sizes of threaded parts allow for a fit that can accommodate a simple, turn by

hand and / or screw driver (similar to ANSI B4.1 RC9 for loose running fits with a hole requirement of

.2220-.2190” compared to a shaft requirement of .2145-.2130” when the nominal size is specified at

.2190”. )

Additionally, it needs to be considered that whenever the adjustable thread ring gage is adjusted, it

applies stress to the adjustment point of the gage being adjusted. Instead of being cylindrical in nature,

the adjustment process forces the gage into being more triangular. While the intent of the relief holes /

cut-outs is to address this issue, the results of the dimensional studies performed show that they are not

fully effective.

The fundamental problem is that adjustable thread ring gages set to thread set plugs, in all likelihood,

DO NOT meet the dimensional tolerance limits of their applicable specifications.

As I mentioned, this is my theory. Like all theories, they require proof before they become fact. I'd like

to share with you at this time the proof that supports this theory:

1A study of 30 adjustable thread ring gages was performed using the Master Scanner to obtain

measurements of pitch diameter and minor diameter. Of these 30 adjustable thread ring gages, not a

single gage was found to meet both tolerance for pitch diameter and minor diameter. Gages used for

this study were all 60° Unified Screw threads and encompassed a range of TPI's, classes of fits, and

nominal sizes. Out of the 30 adjustable thread ring gages, only one gage was found to have a pitch


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diameter within dimensional limits (approx. 97% failure rate), however, the minor diameter was found

out of tolerance, so it could not be considered as meeting specifications. Out of the 30 adjustable thread

ring gages, only 10 were found to have minor diameters within dimensional limits (approx. 67% failure

rate), however the pitch diameters were out of tolerance, so these gages could not be considered as

meeting specifications. This study showed that 100% of the thread ring gages analyzed failed to meet

specifications. Measurement results are shown below, as deviation from nominal):

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1A 2nd

study was performed where an adjustable thread ring gage was properly set to the correlating

thread set plug and then measured at various points around the perimeter of the diameter. Again, this

ring was found out of tolerance for all pitch diameter measurements, regardless of where the

measurement was taken. The interesting thing about this particular study was the interaction between

the pitch diameter readings and the minor diameter readings. Where the PD's were found larger, the

minor diameters were found smaller. Results are charted results below:


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1A 3rd

study was performed using this same adjustable ring gage where it was continuously adjusted

until it the Pitch Diameters and and Minor Diameters were brought as close as possible to reading

within tolerance, as unfortunately both could not be adjusted in. The closer the PD's were brought into

meeting tolerace, the tighter the ring was to the set plug. At the point where both the PD's and Minor

Diameters were adjusted into being as close as possible to the defined dimensional requirements, the

ring was so tight on the thread set plug it took as much as 55 in/lbs of force to be applied to thread onto

the set plug with mechanical assistance. This, of course, does NOT meet the requirements of “slight

drag.” (This can also further substantiate the comparison to the ANSI B4.1 LN 1, Locational

Interference fit mentioned earlier.) When this thread ring was correctly set to the correlating thread set

plug only 2-5 in/lbs of force was required to achieve the “slight drag” requirements.

Conclusion and Next Steps

So what does all this mean? I suppose it all depends on what your role is in regards to threads, thread

gaging, and thread specifications. Does this mean that all adjustable thread ring gages are “bad”? I

try to avoid the word “bad” when evaluating for conformance to specifications. I prefer the terms

“within tolerance / out of tolerance” and / or “meets specifications / does not meet specifications.”

Adjustable thread ring gages can still be used and are a good tool for evaluating thread functionality,

however, they most likely will NOT meet the dimensional specification requirements. Please see the

following pages for recommendations.

For the manufacturer using thread gages to inspect thread products you are producing:

If you need to ensure that your thread products not only work properly, but also need to ensure

that the product meets specification requirements, be knowledgeable of thread specifications

and specifications of the gages being used. Ensure that your gages are calibrated and adequate

for the jobs you are running. The author not only recommends inspecting externally threaded

parts with fixed (IE non-adjustable) thread ring gages, but also verifying parts produced for


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major diameter with a micrometer and pitch diameter with a johnson gage roll comparator or by

using the 3-wire method with a super micrometer, if a Contact Scanner cannot be purchased. If

you are using adjustable thread ring gages to inspect threaded parts produced it is absolutely

critical that you inspect the major diameter and pitch diameter as described above. It is also

critical that you also own the correlating thread set plug so that the adjustable thread ring gages

can be set correctly and periodically evaluated to ensure they are acceptable for use. The thread

set plug should be sent in to a calibration laboratory for periodic calibration. If you feel

confident setting and adjusting the thread ring gages yourself you may choose to perform this

action yourself, rather than sending the ring gage in for calibration. If you do not feel confident

in setting and adjusting thread rings gages, they should be sent into a calibration laboratory for

service at the same time as the correlating thread set plug. If your company owns an adjustable

thread ring gage, it is absolutely critical that you also own the correlating thread set plug. Due

to the shear number of different thread sizes, pitches, classes of fit, configurations, and custom

pitch diameters available it is absolutely impossible for a single calibration laboratory to own

every possible correlating thread set plug. Adjustable thread ring gages can also be calibrated

using a contact scanner (if your calibration provider has one available for use), however, as

shown they will most likely be found out of tolerance using this method.

It also needs to be strongly re-iterated that simply using Go / NoGo Thread Ring Gages is not

an adequate way to determine the acceptability of manufactured externally threaded

components. This is true regardless of whether the rings are fixed or adjustable. Go / NoGo

Thread Ring Gages should be used as more of a functionality check and other methods, as

previously mentioned, need to be employed to determine acceptability to specification

requirements.

For the calibration laboratories calibrating thread ring gages:

The author recommends utilizing the Contact Scanning method for calibration. If a Contact

Scanner is used, report your measured values and if they are out of tolerance to specifications,

list them as such. It does no good to the user of these thread ring gages to just know reported

actual values. They need to know if the thread ring gage they have purchased and are using

meets specifications. Additionally, if enough thread ring gages are found to be out of tolerance,

this will bring further attention to this issue and it will need to be addressed by the

manufacturers and the ASNI/ ASME advisory boards. This will, hopefully, drive changes to

specifications and / or methods to which these units are produced and inspected.

If a Contact Scanner cannot be purchased for use, a thread set plug must be used for calibration.

Since this is a tactile calibration, it is strongly recommended it is listed as such on the

calibration certificate. It is also recommended that any numeric measurement results reported

are clearly defined as having been obtained from the thread set plug and not the thread ring

gage itself.

For the manufacturer producing thread gaging products:

The author strongly recommends purchase of a contact scanner to measure thread plugs, set

plug, and ring gages to ensure that they meet specifications. It is also recommend to only offer

fixed ring gages, as they have proven more reliable in meeting dimensional requirements. If


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neither of these are options for your company it is absolutely imperative that the method of

inspection and qualification of the adjustable thread ring gage is clearly defined. It is also

strongly recommended that a correlating master thread set plug is offered at the time of

purchase of adjustable thread ring gages and they are ONLY sold as sets.

For the members of the ANSI / ASME advisory boards for thread specifications:

With this information being presented and further studies in process, specifications on thread

ring gages absolutely need to be reviewed and reconsidered. It is pointless to have

specifications that cannot be achieved. It is the authors recommendation that this issue can be

addressed by one or more of the following approaches:

o Adjustable thread ring gages specifications be revised to allow for achievable

dimensions that will still work for allowing only acceptable products or to list the Pitch

Diameters and Minor Diameter requirements as reference only dimensions with no

tolerance applied.

o Adjustable thread rings gages have the current specification applied to them for the

purpose of the manufacture of these gages only. The manufacturer would then be

required to list the measurement results utilizing a Contact Scanner. After initial

manufacture and first article inspection of each and every gage produced, subsequent

inspections, setting, and or adjustment would need to be done using the correlating

thread set plug. It would need to be a requirement that thread set plugs are supplied at

the time of purchase of the adjustable thread ring gage and that adjustable thread ring

gages are only sold as a set with the correlating set plug.

o Adjustable thread ring gages are designated as obsolete and fixed thread ring gages take

their place.

References

ANSI / ASME B1.1 Unified Inch Screw Threads

ANSI / ASME B1.2 Gages and Gaging for Unified Inch Screw Thread Series

Euramet cg-1 Determination of Pitch Diameter of Parellel Thread Gauges by Mechanical

Probing

ANSI / ASME B4.1 Preferred Limits and Fits for Cylindrical Parts

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