JMPF 5.56 Knurled 1/2-28 x .635 OD x 5/8 long Aluminum Thread Protector Adapter 5.56/223 Made in the USA, not China like others Made from lightweight 6061 aircraft grade aluminum .635 OD x 5/8 long x 1/2-28 thread Click on JMPF to view our other parts/sets