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When your CNC router, 3D printer, or linear actuator suffers from shaft wobble, binding, or premature wear, the culprit is often an undersized or unsealed bearing. Engineers, makers, and machine builders who demand repeatable, low-friction linear travel need a sealed linear ball bearing they can trust across a wide range of shaft diameters.
These linear ball bearings are manufactured from chrome steel (GCr15) with a sealed design that retains grease and blocks contamination. Available in sizes from LM4UU (4 mm bore, 8 mm OD, 12 mm length) through LM20UU (20 mm bore, 32 mm OD, 42 mm length), with specialty variants LMH8UU and LMH8LUU for extended-length applications. Sold individually or in packs of 5 or 10 for multi-axis builds.
Typical use cases include: linear ball bearing for 3D printer X/Y/Z axis (LM8UU is the most common RepRap standard), CNC router carriage guide rail systems using LM12UU or LM16UU, and robotic arm linear slide assemblies where LM10UU or LM13UU provide the right bore-to-load balance.
Covers LM4UU through LM20UU plus LMH8UU and LMH8LUU — one source for your entire multi-axis build.
Integrated rubber seals on both ends retain lubrication and exclude dust, chips, and moisture for longer service life.
Precision ball tracks enable smooth, consistent linear travel with minimal stick-slip — critical for accurate CNC positioning.
Manufactured to standard LM-series tolerances so bearings drop into compatible housings and pillow blocks without modification.
Order 1, 5, or 10 pieces per size — ideal for prototyping single axes or stocking a full multi-printer workshop.
Suited for 3D printers (RepRap, Prusa, Ender-style), CNC routers, laser cutters, linear actuators, and robotics platforms.
| Bearing Type | Linear Ball Bearing (LM-series) |
|---|---|
| Available Sizes | LM4UU, LM5UU, LM6UU, LM8UU, LM10UU, LM12UU, LM13UU, LM16UU, LM20UU, LMH8UU, LMH8LUU |
| Bore Diameter Range | 4 mm – 20 mm (see variant options) |
| Outer Diameter Range | 8 mm – 32 mm (see variant options) |
| Length Range | 12 mm – 42 mm (see variant options) |
| Material | Chrome steel (GCr15) bearing body; rubber seals |
| Seal Type | Double-sealed (both ends) |
| Lubrication | Pre-greased |
| Compatible Shaft Type | Hardened smooth linear shaft |
| Pack Quantity Options | 1 pcs / 5 pcs / 10 pcs |
| Weight (per piece) | See variant options |
Match the bearing bore to your shaft diameter exactly. For example, an 8 mm shaft requires LM8UU (8 mm bore, 15 mm OD, 24 mm length). Check your machine's specification or measure the shaft with calipers before ordering. The variant option names include bore × OD × length in mm for easy reference.
Both fit an 8 mm shaft, but LMH8UU has a larger outer diameter housing compared to the standard LM8UU. This makes LMH8UU suitable for applications requiring a wider bearing seat or higher radial load capacity. LMH8LUU is the long version of LMH8UU, offering greater contact length for improved stability.
Yes. LM8UU is the standard linear bearing used in most RepRap-derived printers including Prusa i3 variants and Creality Ender-series machines. LM6UU is commonly used on smaller delta printers. Always verify your printer's carriage housing inner diameter matches the bearing's outer diameter before installing.
Sealed bearings have a marginally higher initial drag than open bearings due to seal contact, but this is negligible in most CNC and 3D printing applications. The seals significantly extend bearing life by keeping lubricant in and contaminants out, making them the preferred choice for workshop environments.
Linear ball bearings are designed primarily for radial loads during linear motion. They are not intended to carry significant axial (thrust) loads. For applications with combined loading, pair with appropriate end stops or thrust bearings to protect the linear bearing from axial forces.
A standard Cartesian 3D printer typically uses 6–12 LM8UU bearings (2–4 per axis). A CoreXY build may use fewer. CNC routers vary widely by design. Ordering a 10-pack is cost-effective for full builds or to keep spares on hand for maintenance.
These bearings come pre-greased from the factory. For most applications they can be installed directly. In high-cycle or high-speed environments, adding a small amount of compatible lithium grease through the seal gap every few months will extend service life.
