For positive measurement O-Rings every time, you can use Nimax O-Ring identification gauge for accurate measurements of O-Ring I.D.

Slide gauge for measuring O-Rings up to 13″ inside diameter.
Measures AS568A dash series, -001-050, -102-178, -201-279, -309-382 and -425-455

Please check below link

O-RING MEASURING GAUGE