Features: Improves cycling and overall operation Improved recoil spring life Hardened stainless steel guide rod machined from barstock .250” Rod Diameter Full size features a 17# chrome silicon flat wire recoil spring Compact size features a 22# chrome silicon flat wire recoil spring Full size is compatible with standard recoil spring plugs and Shok-Buff Recoil Buffers Compact model includes hardened stainless steel reverse spring plug and has a guide rod which is clearance for compact barrel lugs and link