Use these screw-in end caps to dress up and provide protection for the end of your YHM forearm. Does not interfere with the free floating of your barrel and helps keep out debris. Drilled to allow for proper heat venting. Both models fit all hand guards that will accept our end caps. The "B" model is for heavy barrels and has an inside diameter of 1.050 inches, and the "A" model is for all other barrels and has an inside diameter of 0.925 inches.