FEATURES: Knurled exterior Machined from Stainless Steel Available for the following threads 1/2"-28, protector has a .570 OD 9/16"-24, protector has a .633 OD .578"-28, protector has a .650 OD BENEFITS: Prevents the threads on your barrel from becoming damaged when a muzzle device is not installed Especially handy when switching muzzle devices Knurled exterior makes these easy to install and remove Mfg: Yankee Hill Machine Co., Inc.