Primary Weapons Systems Piston Fits 1/2X28 Anodized Finish Black. Starting out by producing muzzle devices they tested their compensators on all different types of rifles - from M4s to AK-47s. After using both styles of rifles in testing with high round counts the difference in maintenance needed was both astounding. From that basic realization the PWS long-stroke piston system was born; keeping the core values of the AR-15 design while also lessening the need for maintenance in high-volume fire situations and adverse conditions. The 1/2x28 piston allows the use of PWS suppressors on 1/2x28 threads. Specifications for Primary Weapons Systems Piston: Manufacturer: Primary Weapons Systems Color: Black Finish: Anodized Threads per Inch: 1/2x28 Features of Primary Weapons Systems Piston Fits 1/2X28 Anodized Finish Black: 1/2x28 Package Contents: Primary Weapons Systems Piston Primary Weapons Systems Piston Fits 1/2X28 Anodized Finish Black PISTON-1-2X28