Fix-a-THRED® inserts are made from high-quality, 18-8 (Type 304) diamond-shaped stainless steel wire. While the inserts are slightly larger in diameter than the tapped hole, the insert is compressed during installation, and then expands, permanently locking into place. The spring-like design of the insert spreads the load over the entire bolt and the hole, reducing stud fracture and increasing holding or pull-out strength.