LM12UU linear bearing for 12 mm smooth shaft – 12 × 21 × 30 mm

The LM12UU is a recirculating-ball linear bearing designed to travel along 12 mm precision smooth shafts. It is used in linear motion systems for 3D printers, CNC machines, laser engravers, plotters, automation equipment and custom mechanical projects.

Its cylindrical body can be installed in a commercial bearing holder or a custom housing designed for the project. Unlike an SC12UU unit, this product is supplied without an external aluminium housing.

Nominal LM12UU dimensions

• Nominal inner diameter: 12 mm.
• Nominal outer diameter: 21 mm.
• Nominal length: 30 mm.
• Type: cylindrical linear ball bearing.
• Format: LM12UU.

These dimensions correspond to the usual LM12UU dimensional standard. However, because the specific manufacturer is not identified, tolerances, internal clearance and secondary details may vary between batches. If the housing fit is critical, measure the received unit before machining it.

Shaft and housing compatibility

It is designed for 12 mm nominal diameter precision smooth shafts, such as the cut-to-length 12 mm precision smooth rod.

It should not be used on threaded rods, uncalibrated bars or shafts with rust, dents or surface damage. An unsuitable surface may cause noise, play, binding or premature wear of both the bearing and shaft.

Housing compatibility must be checked using the three main dimensions: 12 mm inner diameter, 21 mm outer diameter and 30 mm length. Matching the shaft diameter alone does not guarantee that the bearing will fit every housing.

Installation recommendations

• Install the bearing in a correctly aligned cylindrical housing.
• Avoid deforming the outer sleeve through excessive interference or clamping force.
• Use an appropriate axial retaining system to prevent the bearing from moving inside its housing.
• Keep the shaft clean and use a lubricant suitable for linear ball bearings.
• Check that movement is smooth by hand before operating the motors.
• Carefully align the shafts when several bearings are used on the same carriage.

A small alignment error may cause two bearings that move correctly separately to bind after being secured to the same structure.

Mounting alternatives

When a unit prepared for direct carriage mounting is required, consider the SC12UU with aluminium housing, which integrates a bearing for a 12 mm shaft inside a machined block.

For a greater guiding length, the LM12LUU long linear bearing is also available. The long version is not dimensionally interchangeable with the 30 mm LM12UU and requires a different housing.

For a polymer sliding alternative, consider the Igus DryLin RJ4JP-01-12. It shares the nominal LM12UU envelope but works differently: it uses sliding contact rather than recirculating balls, and its fitting, clearance and alignment requirements are not necessarily identical.

Package contents: 1 LM12UU linear bearing.