Tandemkross’s replacement firing pin rebound springs for Ruger® Mark-series pistols meet factory specs for tension and fit in the gun. The popular Ruger .22 LR "Mark" pistols are prized for their strength and reliability, but in time any spring will wear out, become weak, or even break. When that happens to your the firing pin rebound spring of your Mark I / II / III / IV pistol, restore its function with a Tandemkross replacement. Meets factory specs for correct spring force Easy, drop-in installation - no tools needed Sold in a pack of 5 Having a pack of Tandemkross replacement firing pin rebound springs in your range bag means a shooting session doesn’t have to be scrubbed for lack of a simple, inexpensive, easy-to-install part. Fits the following pistols: Ruger® Mark I™ Ruger® Mark II™ Ruger® Mark II™ 22/45™ Ruger® Mark III™ Ruger® Mark III™ 22/45™ Ruger® Mark III™ 22/45™ Lite Ruger® Mark IV™ Target Ruger® Mark IV™ Hunter Ruger® Mark IV™ Competition Ruger® Mark IV™ 22/45™ Tactical Ruger® Mark IV™ 22/45™ Lite