HK Heckler & Koch HK Pin - Roller - Locking - Bolt Heads
HK roller retainer pin or clamping sleeve (holds roller retainer plate in place). Each retainer pin works with all roller retainer plates & springs. All 3 types including oval-shaped roller retainer plates, roller retainer "S" springs, and the latest style roller retainer F plates.
1st Gen Oval Shaped Bolt Head
2nd Gen Roller Retainer Spring
3rd Gen Roller Retainer Plate