Precision locknuts are used to adjust, preload, and secure bearings, gears, and other power transmission products to shafts and spindles with a high degree of stiffness. They have machined internal threads and sturdy faces that provide strong metal-to-metal locking without distortion. Precision locknuts are sometimes referred to as bearing locknuts since the dimensions of these locknuts are made to correspond with standard bearing sizes. Most precision locknuts are tightened with a spanner wrench. Right-handed threads are tightened with clockwise turns. Left-handed threads are tightened with counterclockwise turns. Typically, setscrews on the face or periphery of the locknut are used to lock the female threads of the locknut to the male threads of the shaft.


Most precision locknuts have a locking method that secures the locknut to the shaft.  Locking methods include setscrews, clamping screws, shoes and resilient ring.  Setscrews can either be located on the periphery or the face of the locknut.  In either method, the setscrew is used to secure the locknut thread to the shaft by distorting the threads. Precision locknuts with a clamping screw have a clamping and a locking section, separated by a radial groove.  Setscrews located on the face of the locking section eliminate the thread clearance of the locknut.  Locknuts with shoes are locked in place by tightening setscrews on the periphery of the locknut, which force a shoe into the threads on the shaft. In the resilient ring locking method, nylon or other resilient material, is pressed between the thread flanks.  If there is no integral locking feature, a lock washer or locking adhesive is often used.   


Precision locknuts are made of stainless steel, hardened alloy steel, or heat-treated alloy steel and are often coated with a black oxide finish for improved corrosion-resistance. They are specified in English units such as inches (in) or metric units such as millimeters (mm) or centimeters (cm). Important dimensional specifications include major thread diameter, threads per inch (English), threads per pitch (metric), locking face diameter, overall locknut diameter, locknut width, and bearing bore size. Holes and slots are located on either the face or the periphery of the precision locknut. Most English threads are non-standard fractional sizes such as 1.767” and 2.360”. Many metric threads comply with shaft tolerance standards such as ISO H5. Thread standards such as Unified Coarse (UNC) and Unified Fine (UNF) are also available for precision locknuts.