How to find the right Linear Ball Bearings AI guide
Written by an AI model from its trained knowledge.
What the AI looks for in Linear Ball Bearings
- Size and series
- Match the shaft diameter, outer diameter and length to the housing. In the LM series, for example, LM8UU means an 8 mm bore and a 15 mm outer diameter. LME and inch series use different dimensions. LM, LME and inch series bushings with the same nominal bore are not interchangeable in the same housing.
- Shaft fit and hardness
- Use a case-hardened, ground shaft around 58 to 60 HRC or harder, with a tolerance class the maker specifies (commonly g6 or h6). Shaft tolerance sets the running clearance, and a soft shaft wears quickly.
- Closed, adjustable or open type
- Choose closed for fully supported ends only. Choose open (OP) when the shaft is continuously supported. Choose adjustable (AJ) for setting clearance. Only open bushings can pass over continuous shaft supports, which long spans need to avoid sag.
- Flange and housing style
- Choose plain, flanged (LMF/LMK-type round or square flange) or pillow-block housed units based on how the bearing mounts. Flanged and housed units avoid machining a precise bore in the carriage.
- Seals and retainer
- Prefer double seals (UU) in dirty environments. Steel retainers suit higher temperatures than resin retainers. Seals keep grit out, and resin retainers can soften with heat.
Brands that matter
- THK: Long-standing LM-series ball bushings.
- NSK: Standard and high-precision linear ball bushings.
- Thomson: Ball Bushing line, strong in inch sizes and self-aligning designs.
- Bosch Rexroth: Linear bushings including self-aligning and segmented designs.
- Schaeffler (INA): Linear ball bearings and housed units.
- Misumi: Configurable flanged and housed bushings.
- igus: Polymer plain-bearing alternative (drylin) where lube-free running matters more than low friction.
What to avoid
- Bulk no-name LM8UU-type bushings in precision machines, because ball quality and clearance are inconsistent.
- Using two widely spaced closed bushings on a long unsupported shaft that sags.
- Over-tightening housing set screws, which distorts the bushing and causes binding.
Questions
What does UU mean in LM8UU?
It denotes seals on both ends. A single U means one seal, and no suffix means open ends.