CARVER Custom Tungsten Guide Rod (with stainless back cap) assembly fits all M&P Competitor Models. You are purchasing the guide rod with your spring of choice. The CARVER Custom Tungsten guide rod can be used with  ISMI "flat wound" recoil spring,

CARVER Custom Tungsten guide rods provide a decisive advantage for all M&P owners by providing an additional 67% weight difference at the front of the pistol versus a stainless guide rod. This extra weight will help reduce muzzle rise allowing quicker follow up shots. Special features include a rigid Tungsten body that improves lock up by completely removing "guide rod flex". The hex screw removable tip allows the user to choose various spring weights that will calibrate the ammunition to the gun.

Used by Law Enforcement and competitive shooters world wide, will not chip or crack like the factory plastic guide rods are prone to. Will not damage or wear your polymer frame and guaranteed to provide a lifetime of reliable service. Weight Difference between Stainless Guide Rods VS Tungsten Guide Rods Stainless M&P Competitor" vs Tungsten M&P Competitor" 0.544 oz1.088 oz *These weights do not include the springs, guide rod weight only CARVER Custom recommends the use of Blue Loctite on the hex screw threads. This will provide a firm hold and still allow easy removal when necessary. Allen wrench provided.