Not to be confused with ordinary sheet metal screws, Chota “STL” Cleats are case-hardened steel and feature a specially designed head that is dished out to form two semi-circular, deep-biting blades. Special “Anti-Back-Out Grooves” on the flange keep the “STL” Cleats securely seated to the Cleat Base. (Required tools: 1/4" nut driver.)