M16 x 1 Left Hand barrel Thread protector. It is machined from US made steel to very high quality standards on CNC lathes in my shop. It has a durable black oxide finish. It is designed for metric threaded barrels. Will fit Glock , Heckler and Koch, Beretta and more. Length is .525" Outside diameter is .730 With a clean crisp knurl. Please confirm your thread size before ordering.