USA
HK
MX
036-I-BO-BL-ST-VO-TO
Old Version smaller and thinner then new version.
OD: .5" 12.7mm Thick: 5/64" .078" 1.98mm
For internal air uses the same o-ring for front and back.
For external air (bottom line), the rear uses the Tombstone Seal / Valve O-ring, Tippmann Part 02-72