1/2 - 28 Threaded barrel protector. It is machined from US made steel to very high quality standards on CNC lathes in my shop. It is counter bored to accommodate barrels that are not undercut at the shoulder. It also has a durable Black Oxide finish. Length is .62" Outside diameter is .630 With great looking machined grooves. The only ones like it! 100% Made in the USA! Please confirm size before ordering.