For zero setting of inside micrometers, three points internal micrometers and bore gages.
Deviation is the difference between the ordered size and the size marked on the setting ring when supplied.
For example, the ordered size is .2”, the size marked on the setting ring when supplied may be .20008″.

Insize 4121-7D2, AMERICAN STANDARD THREAD RING GAGE, GO, 7/16-20UNF, 6928640359279
3M 26138, PPS Series 2.0 Adapter, Type S42, 3/8 Female R-Angle, 19Thread BSP, 7100135930 