US made from US steel, this low carbon steel insert (1018) fills the thumb slot on a Mauser rifle to make a solid side wall. Work must absolutely be done by a knowledgeable welder, and preferably gunmaker. You will absolutely warp your action if you are not careful.

Please note, there are multiple forms of thumb slots, this fits the most common, Vz.24, Brazilian 1908, Argentine 1909, etc. The thumbslots themselves vary and you may have deepen your chamfer for your root pass to get 100% fill.