1/2" X 28 barrel thread and crown protector. It is machined from stainless steel to very high quality standards. It is counter bored to accommodate barrels that are not undercut at the shoulder. It extends over the end of the barrel to protect the barrel crown if dropped. It has a smooth outside for a seamless look. It has 9/16" wrench flats for easy installation and removal. Length is .475" Outside diameter is .640. Please confirm your thread size before ordering. 100% made in the USA! Many more items on our website!