The longest lasting handgun recoil spring made - our testing has indicated that these springs have a service life up to ten times greater than conventional coil springs. Features: Improved recoil spring life Recoil spring guide machined from barstock 1/4 inches rod diameter 17# flat-wire recoil spring Compatible with standard recoil spring plug Compatible with Shok-Buff recoil buffers Recommended use - full-size 5 inches 45 ACP shooting 230 grain hardball equivalent or standard pressure JHP self-defense ammunition with a power factor of 175,000 to 195,000 Average service life - 40000 rounds