Wilson Combat's flat-wire recoil spring kit, .45 ACP, 17 Lb. recommended use: full-Size 5" .45 ACP shooting 230 gr. hardball equivalent or standard pressure JHP self-defense ammunition with a power factor of 175,000 to 195,000 (Velocity x Bullet Weight = Power Factor). The average service life is 40,000 rounds. Improves cycling, overall operation and recoil spring life. Compatible with standard recoil spring plug and Shok-Buff recoil buffers. Includes .250" rod diameter and 17# flat-wire recoil spring.