Our high quality round wire recoil springs are color coded for easy identification. No more counting coils or guessing if you have the correct spring. The red spring is 14 lbs and is ideal for hot 9mm, 40 S&W or 45 ACP. Blue spring is 12 lbs and ideal for standard velocity 9mm. Coating on the spring will typically last 3000 cycles which is our recommended life of the spring.. ZEV recoil springs will work in captured and uncaptured guide rods. When using a captured guiderod you will also need the ZEV spring retaining washer. NOT RECOMENDED IN COMPACT GLOCK - G19 G23 G32 STOCK SPRING WEIGHTS: the full size models, 17, 20, 21, 22, 24, 31, 34, 35, 37, utilize a spring weight of 17 pounds. Compact models, 19, 23, 32, 38, use 18 pound springs. Sub-Compact models, 26, 27, 33, 39 utilize a 16 pound spring and Sub-Compact large frame models, 29, 30, 36) utilize a 17 pound spring. If you only shoot standard ammunition is recommended that you use the stock spring weight. If you are shooting custom hand-loaded ammunition and maybe use a compensator, experimenting with another spring weight is a must.