This is a CMMG Takedown Pins known as the Mk3, model 38AFF31.
These improved pins are slightly longer to make take down much faster and easier. The ends have a divot to allow the use of a bullet tip without the fear of slipping. Used on the Mk3 platform that is based on the LR308 patterned .308 rifle.
Features:
Faster and easier takedown
Fits LR308 patterned .308 rifles
Divot to allow the use of a bullet tip