Spline Nut: What It Is and How to Select One

Answer: A spline nut - also called a spline sleeve - is the nut component of a ball spline. Steel balls circulate inside its spline grooves, so the nut can transmit torque while moving linearly along the shaft, in any orientation. To select one you specify four things: shaft diameter (2-100 mm at UVT), preload class (T0 clearance / standard / T1 light preload), precision grade (standard / H / P), and mounting type (round flange, cut-edge flange, block). UVT spline nuts and shafts carry interchangeability marks (S1 / S2) and are stocked as separate items, so nut and shaft can be paired freely.

How a spline nut works

The nut houses a ball retainer; steel balls run between the nut's spline grooves and the shaft's precision-ground spline grooves. Because the grooves are axially cut, the nut is free to travel linearly, and because they engage the shaft profile, torque is transmitted through the balls at the same time - this is what distinguishes a spline nut from a ball bushing (linear only) or a plain keyway (no rolling linear motion).

Spline nut selection checklist

Interchangeability saves inventory

UVT marks each spline nut and shaft with an interchangeability grade (S1 / S2): within the same grade, any nut fits any shaft. Nuts and shafts are stocked separately, so an urgent change does not wait on a matched pair - a documented advantage for machine builders that carry spares.

Typical applications

• SMT mounter nozzle Z-axis (limited stroke spline nut)
• Semiconductor packaging and IC test handlers (miniature 3 mm)
• SCARA and assembly robot Z-axes (spline nut with T1 light preload)
• Machining center ATC and tool change mechanisms

For the full spline nut range and miniature series see our product overview and the miniature ball spline page; selection tables and preload guidance are on our technical support page. UVT Transmission - precision spline nuts for semiconductor, SMT, robotics and medical equipment.