5/8" x 24 Bull Barrel Thread 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. With a durable black oxide finish. Smooth outside for a seamless look. Machined with care for a great fit and finish. Length is .625" Outside diameter is .930. 100% Made in the USA!