THKLM50UURecirculating Ball Bushing — 50 mm Shaft, 80 mm OD, 100 mm Long, Six Ball Rows, Sealed Both Ends (Shaft Not Included)

Product Description

What this part is

A THK Linear Bushing, model LM50UU: a recirculating ball bushing that runs on a cylindrical hardened shaft. Six rows of balls circulate in a moulded retainer inside the nut; in the loaded zone the balls are in point contact with the shaft, which is what gives the very low friction and the smooth, quiet travel this family is known for. The nut body is high-carbon chromium bearing steel (SUJ2), hardened and ground on both the bore and the outside diameter.

Decoding the designation

LM is the standard metric Linear Bushing series — the plain cylindrical form, with the most accurate outside diameter in the range. 50 is the nominal shaft diameter in millimetres, which is also the inscribed bore. UU is the contamination protection code: a synthetic rubber seal fitted at each end of the nut. Suffixes you may see on neighbouring parts change the part fundamentally: -AJ is the clearance-adjustable form with a slit along the nut, -OP is the open form cut away by one ball row for use where the shaft is supported from below, -L is the long form containing two retainer assemblies, and -GA substitutes a metal retainer for high-temperature work. LM50UU carries none of those, so this is the plain standard sealed bushing.

Scope — what is in the box

The bushing only. The hardened and ground LM shaft is not included, nor is a housing, snap ring, stopper plate or shaft end support. A ball bushing is not usable on ordinary bar stock — the balls roll directly on the shaft, so the shaft must be a dedicated hardened, ground LM shaft to the correct tolerance or the balls will indent it within hours.

Published ratings and mounting data

Nominal shaft diameter / inscribed bore: 50 mmOutside diameter: 80 mmOverall length: 100 mmRows of balls: 6Basic dynamic load rating C: 3 820 N (3.82 kN)Basic static load rating C0: 7 940 N (7.94 kN)Mass: 1 418 gRetainer: integrally moulded synthetic resinNut material: SUJ2 high-carbon chromium bearing steel, ground bore and ODSeals: synthetic rubber, both ends (UU)Equivalent factor K for moment calculation: 0.096 single nut, 0.032 for two nuts in close contactRecommended housing bore: H7 for a loose fit, J7 for a transition fitRecommended shaft tolerance: f6 or g6 for normal clearance, h6 for a small gapRetaining snap rings: 80 mm C-shape, outer surface or inner surfaceMaximum service temperature: 80 °C with the resin retainer

What these specs mean in practice

The load rating quoted is for one ball row directly under the load. Rotate the bushing in its housing so that two rows share the load and the effective rating rises — THK’s own factor for a six-row bushing is 1.28 times C. That orientation choice is free capacity and is routinely missed. The bigger practical constraint on a round-shaft bushing is moment: a single bushing on a shaft resents any overhung load, and the standard fix is two bushings on the same shaft spaced as far apart as the design allows, which is why THK publishes a separate equivalent factor for the double-nut case. The 80 °C ceiling is a hard limit set by the resin retainer, not a guideline; above it the part number to use is LM50GA with a metal retainer.

Fitting notes

Retain the bushing axially with a snap ring or a stopper plate. Never secure it by driving a set screw against the outside diameter — a single screw distorts the thin nut wall and pinches the ball path, and the bushing will feel rough immediately. When pressing it into a housing, use a jig or a flat plate against the nut body, not against the side plate or the seal. Insert the shaft square to the nut and push it straight in; entering at an angle drops balls or deforms the retainer. Remove the anti-rust oil and charge with a lithium-soap No. 2 grease before use, and do not rotate the bushing on the shaft — it is a linear device only.

Interchange guidance

Also written LM-50-UU, LM 50UU, LM50-UU and LM50. The metric LM series is the one used most widely in Japan; the equivalent-envelope European metric series is LME, and LME50 is a different bore-to-OD relationship, so LM and LME are related sizes, not substitutes. The inch-series equivalents from Thomson, PBC and RBC round-shaft bushings do not match either the OD or the length. Within the LM50 size, LM50-AJ (clearance adjustable), LM50-OP (open) and LM50L (long, two retainers) are separate parts with different capacities, and LM50GA is the metal-retainer high-temperature build.