Schuster MFG M1 Gas Nut Adjustable Made from hardened tool steel and parkerized. Service rifle legal! Has the same appearance and configuration as original; CMP 4th Edition #4-13-2-b. By adjusting the volume of gas in the cylinder you change the speed of the op-rod and the harmonics of the barrel. If you want to tame things down, it can be opened up just enough to function, or opened fully for single shot functionality. If you are working on your own hand loads, a quarter turn WILL affect group size. If you have a 308 Garand this is a necessity if you want to safely shoot heavier 168 grain match bullets. Also a must have if you hunt with your CMP Garand but want to shoot heavier 30-06 loads. Includes instructions and the adjustment tool (Allen wrench). Made in the USA. Lifetime factory warranty. Technical Information Material: Parkerized Hardened Tool Steel Notes: This version has 4 gas ports This modification is Service Rifle Legal. Same appearance and configuration as original per CMP rules - 4th Edition 4-13-2- b. Please Note: This accessory is not legal for As-Issued matches. $34.00