Heat and vibration can loosen bolts, requiring regular maintenance to retorque them. Unfortunately, retorquing often leads to overtorquing, and eventually to failure. To solve that problem, engineers at Stage 8, San Rafael, Calif., designed a locking counterbore bolt. To use it, a small slot is milled next to a counterbored hole. The bolt is torqued to specs, and a locking retainer ring slips over the bolt. A clip then fits into a groove on the bolt head top to hold the retaining ring in place. The design acts like a small wrench locked on the bolt, keeping it from turning.