SKF
Precision Lock Nuts
SKF precision lock nuts are designed for super-precision bearings used in machine tool spindles and other high-accuracy systems. They feature fine pitch threads, precision machining, and face squareness tolerances that minimize runout and ensure uniform clamping force on the bearing inner ring. Variants include KMT and KMTA (with threaded pins for axial locking) and N series with face slots for spanner tightening. The locking mechanism does not induce misalignment, maintaining the spindle’s rotational accuracy. These nuts are essential for achieving the rated performance of high-precision angular contact ball bearings and cylindrical roller bearings in lathe, milling, and grinding spindles. SKF precision lock nuts support speeds up to very high n·dm values and are often supplied with specific tightening torque values to set bearing preload.
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High Face Squareness
Minimizes axial runout, critical for spindle precision.
Fine Pitch Threads
Allow sensitive preload adjustment.
Runout-Free Locking
KMT/ KMTA designs lock without bending bearing ring.
High-Speed Balance
Suitable for spindle speeds up to 1 million n·dm.
Robust Precision Grade Materials
Hardened, ground threads resist wear.
Compatible with Super-Precision Bearings
Matches P4 and P5 bearing tolerance classes.
Achieving Spindle Preload with Precision Lock Nuts
Apply the correct tightening torque to a precision lock nut to set the axial preload on an angular contact pair. SKF provides torque/preload charts based on bearing size. Over-tightening can overload and rapidly overheat the bearing; under-tightening leads to poor rigidity.
KMT vs. KMTA Precision Nuts
KMT nuts use set screws for locking; KMTA nuts use a threaded pin that radially expands a sleeve into the nut body, providing a very concentric lock with minimal runout influence. Selection depends on the spindle’s maximum speed and required balancing grade.