Description Factory Ruger Rebound Spring Support for Mark 1 2 3 4 IV & All 22/45 Pistols Rebound Spring Support (firing pin spring support) fits ALL Mark Series Pistols ever made**. (**The very first 1949 – 1952 production years could differ, best to observe closely on these**) This holds the rebound spring (firing pin spring) sets under the firing pin in the bolt. It often ends up lost or messed up from not being installed properly. These supports vary in thickness from batch to batch, you may need to shape it for your spring to freely slide onto it. If this is beyond your skill set, find a gun smith
