Used on a.r.m.s. item 21 stanag rings and other various 30mm optic sight ring mounts. split ring inserts converts 30 mm ring mounts to 1 inch ring mounts 17b segmented, plain, no outside flanges
Used on c17a acft. 0.9484" overall length press fit undersize i.d. groove/center 0.1250" wide with a radius of 0.094 cadmium surface treated 17c solid, plain, no outside flanges