The True Precision Recoil Spring Kit fits Sig Sauer P365 XL and P365 X-Macro pistols with the 3.7" slide. It lets you tune the recoil spring weight to your ammunition, your muzzle device and how you want the pistol to run. The kit includes five chrome silicon springs, from 12 lb to 20 lb. Chrome silicon holds its rate longer than standard music wire. A lighter spring helps the pistol cycle reliably with light target loads or a compensator that bleeds off gas. A heavier spring slows the slide with hot defensive loads and can reduce muzzle flip. The non-captured stainless steel guide rod lets you swap springs without buying a new assembly for each weight. Features: Fits Sig P365 XL and X-Macro 3.7" slide models 12, 14, 16, 18 and 20 lb springs included High-strength chrome silicon springs Stainless steel non-captured guide rod with screw and bushing 100% made in the USA Change one variable at a time when you tune. Install the new spring and run at least 50 rounds of your carry ammunition to confirm reliable feeding, ejection and slide lock before you carry the pistol.