Suggested Retail Price $21.95 M9 x .75 to 1/2-28 This threaded barrel adapter fits and allows GSG 1911 22, SIG 1911 22, 5PK 22 pistols to use standard U.S. 1/2-28 threaded sound suppressors or other muzzle accessories. Our adapter easily replaces the factory barrel nut and gives you the 1/2 x 28