Perma-Coil helically coiled inserts are made of stainless steel wire that has been rolled to a carefully controlled thread form. When installed, Perma-Coil inserts adjust to a tapped hole, becoming a functional thread with a strength exceeding the original. Perma-Coil inserts and repair kits are designed to repair stripped threads in a variety of metals. Aluminum, aluminum alloys, steel, and cast iron. If the original threads can be stripped, Perma-Coil inserts can repair them. By following the detailed instructions provided with every kit, even an inexperienced do-it-yourselfer can repair stripped threads, permanently. Perma-Coil inserts and tools meet all applicable industrial and military specifications. They may be used on all military and government trucks, aircraft and other vehicles covered by MS 21208 and MS 21209; also NAS 1222 specifications for helically coiled wire inserts. Made in U.S.A. Replacement 1/4-28 x .375 size inserts for kit #PRC1208-204 Qty. Inserts: 12 per pack