These Shooter's Packs are a great upgrade for popular revolvers. Replacement springs improve trigger function for better shooting performance. This pak for rimfire models contains 1 each 9 pound reduced power hammer spring and 1 each 13, 14 and 15 pound reduced power rebound springs allowing adjustment for lighter and smoother trigger and hammer action. Note: Rimfire models 317, 650, 651 have a 12 Lb. factory hammer spring.