This is a Yankee Hill Machine Co Buffer known as the 9MM Bolt Buffer, model YHM-925-A.
Stainless Steel buffer for carbine stocks. Designed with extra weight and length for 9mm. The added length helps prevent breakage of the bolt catch. Includes a mil. spec. bumper. Weight is 5.9 oz.
Features:
Black finish
9MM bolt buffer
Stainless steel