THKLM50ULinear Ball Bushing, 50 mm Shaft x 80 mm Housing Bore x 100 mm Long, Open Circuit Form

Product Description

What this part is

The LM50U is a recirculating linear ball bushing — a cylindrical bearing that slides along a round shaft rather than rotating on one. It fits a 50 mm shaft, drops into an 80 mm housing bore and is 100 mm long. Note what those three numbers mean on a linear bearing: shaft diameter, housing bore, and LENGTH along the shaft — not bore, outside diameter and width.

What these specs mean in practice

How it works. Inside the steel sleeve, rows of balls run in closed circuits — rolling along the shaft under load, then curving out of the load zone and returning through a channel to start again. Because the balls recirculate, stroke is limited only by how long the shaft is, not by the bearing. The balls make POINT contact with the shaft, so friction is very low and identical in both directions, which gives smooth creep-free motion at low speed where a plain bronze bushing would stick and slip.

The trade-offs follow directly from that point contact. Load capacity per bushing is modest compared with a profile-rail block, and the whole load passes through a few small contact spots — so the shaft must be a properly hardened and ground linear shaft. Run one of these on ordinary cold-drawn bar and the balls will indent tracks into it quickly. It is also NOT self-aligning: bushing and shaft have to be genuinely parallel, so on a twin-post arrangement the bores must be properly aligned or one bushing will bind.

Decoding the designation

On seals, and this is the practical difference between this part and its sibling. THK’s UU suffix denotes seals at both ends; the photographs of this LM50U show the ball circuit and retainer OPEN and visible at the exposed end, with no seal covering it. So this is the lower-drag, less protected form. Choose it where the environment is clean and enclosed and you want minimum friction and full usable stroke; choose the both-end-sealed LM50UU where grit or swarf can reach the bushing, because contamination kills a linear bushing long before fatigue does. If your application is dirty, buy the UU.

Quantity and configuration

Sold as one bushing, in its original THK carton.

Interchange guidance

Also written LM-50-U, LM50-U, LM 50U and LM50 U. Central Surplus also stocks the LM50UU form of the same envelope — see that listing if you need seals at both ends.