Sig Sauer MCX Bolt Catch Kit. This bolt catch kit is made of steel OEM factory original Sig Sauer components. Parts in this kit are either unfinished or carry a black finish. This kit includes the bolt catch along with the bolt catch plungers, plunger springs, and pins. This kit contains all the crucial bolt catch parts for the Sig Sauer MCX rifle. These parts are made to the same high standards in material and workmanship as the parts that originally came in your Sig Sauer firearm. This kit is perfect to replace your worn or damaged parts, or to throw in the spare parts chest to always keep your MCX in top operating condition.