Here's a pdf file with the use and care manual of the US Army for the OTV - IBA and SAPI plates. This one was distributed by "Point Blank Body Armor", the first and most known manufacturer of this body armor. This body armor is now out of date. It was then replaced by the IOTV in the US Army, and by the MTV and SPC in the USMC.
Transcript of Use and Care Manual for the IBA - OTV - SAPI (Point Blank)