A lock nut is a type of nut that resists loosening when properly threaded onto a bolt. Nut-and-bolt fasteners are extremely common in industry and home applications. You can learn more in our complete locking nuts guide.Lock nuts fall into one of two groups:● Prevailing Torque Lock Nuts – Prevailing torque is the amount of torque needed to run a nut down a thread on nuts that are designed to resist self-loosening under vibratory forces.● Surface bearing lock nuts – surface bearing – a free spinning nut that requires tightening against a bearing surface in order for the locking mechanism to function.