LM8UU Linear Ball Bearing - 8mm Bore, 15mm OD, 24mm Length

Specifications

• Model Designation: LM8UU

• Bearing Type: Linear Motion Ball Bearing

• Inner Diameter (Bore): 8mm

• Outer Diameter: 15mm

• Overall Length: 24mm

• Seal Type: UU (Double Rubber End Seals)

• Outer Shell Material: Carbon Steel

• Ball Retainer Material: Polymer

• Dynamic Load Rating (C): ~260 N

• Static Load Rating (Co): ~400 N

Key Applications and Projects

• 3D Printers: The absolute standard for X and Y-axis carriage rails on almost all rod-based RepRap and Cartesian 3D printers.

• Desktop CNC Routers: Providing the rigid, low-friction guidance needed for moving Dremels or spindles over a wooden workpiece.

• Automated Pen Plotters: Creating an ultra-smooth, lightweight X/Y gantry to hold a sharpie and autonomously draw complex vector art.

Unlock New Capabilities (Project Evolution)

• The Automated Camera Slider: Ready to upgrade your video production? Buy a pair of 8mm smooth steel rods, four LM8UU bearings, and a 3D-printed carriage block. Mount the bearings into the carriage using zip-ties or snap-rings. Attach a stepper motor to one end of the rails and run a GT2 timing belt to the carriage. Driven by an Arduino and a TMC2208 silent stepper driver, you now have an ultra-smooth, whisper-quiet motorized camera slider for cinematic b-roll and macro timelapses!

Package Includes:

• 1 x LM8UU Linear Bearing (8x15x24mm)

FREQUENTLY ASKED QUESTIONS (FAQ)

1. What does "LM8UU" stand for? "LM" stands for Linear Motion. "8" indicates the 8mm inner bore. "UU" signifies that it has double rubber end seals.

2. What are the exact dimensions? It has an 8mm inner diameter, 15mm outer diameter, and is 24mm long.

3. What kind of rod do I need for this? You must use an 8mm precision smooth rod. Hardened steel or chrome-plated steel rods are required.

4. Can I use these on aluminum or carbon fiber rods? No. The hardened steel balls inside the bearing will quickly dig trenches and gouge soft materials like aluminum, ruining both the rod and the bearing. Use steel rods only.

5. Do these need to be lubricated? Yes! Out of the box, they are typically coated in a thin anti-rust shipping oil. Before use, you should pack them with a light machine oil (like sewing machine oil) or white lithium grease for smooth, quiet operation.

6. Are these bearings directional? No. They are perfectly symmetrical and can be slid onto your 8mm rod from either direction.

7. What are the two grooves on the outside of the metal shell? Those are retaining ring grooves. They allow you to lock the bearing securely inside a tubular housing using standard metal circlips (snap rings).

8. How do I mount this to a 3D-printed part? The most common DIY methods are designing a cylindrical friction-fit housing and pressing the bearing in, or simply using two heavy-duty zip-ties strapped tightly around the metal shell.

9. Can this bearing handle rotational movement? NO. This is strictly a linear bearing. Spinning the shaft inside the bearing (like a drill) will immediately derail the balls and destroy the polymer cage.

10. Are they waterproof? No. While the rubber seals help keep dust out, the high-carbon steel shell and internal balls will rust rapidly if exposed to water or high humidity without heavy grease.

11. Why do they sound "scratchy" or loud out of the box? A "scratchy" sound usually means there is manufacturing dust inside, or they lack proper lubrication. Soaking them in Isopropyl Alcohol to remove the factory shipping oil, letting them dry, and repacking them with lithium grease will usually silence them.

12. Will the balls fall out if I take the bearing off the rod? No, the black polymer cage inside the bearing physically retains the steel balls. You can slide them on and off shafts freely.

13. Can I replace just the internal balls if they get damaged? Practically speaking, no. It is incredibly difficult to rebuild the internal circuits. At this price point, it is always better to just replace the whole bearing.

14. What is the difference between an LM8UU and an LM8LUU? The "L" in LUU stands for "Long." An LM8LUU is essentially a double-length version of this bearing (45mm long instead of 24mm) for handling heavier, wider loads.

15. What does the black rubber ring on the ends do? It acts as a physical wiper. As the bearing moves, it wipes dust and debris off the steel rod so it doesn't get ground into the ball tracks.

16. How much weight can a single LM8UU handle? It has a dynamic load rating of approximately 260 Newtons (about 26 kg / 58 lbs). However, for maximum lifespan and smoothness, you should use multiple bearings to distribute loads.

17. Can these handle side-loads (twisting forces)? Linear bearings are designed for direct radial loads. Strong twisting forces (moments) will cause them to bind and scrape against the shaft. Always use them in pairs or sets of three/four to prevent twisting.

18. Are these compatible with an original Prusa i3 MK3S? Yes, the LM8UU is the exact dimension and specification required for standard Prusa i3 X and Y-axis rail assemblies.

19. Why is there a slight gap between the balls in the internal tracks? A tiny amount of clearance is required so the balls don't grind against each other as they round the tight corners of the recirculation return track.

20. How do I properly press this into an aluminum block? If press-fitting it into an SC8UU block or custom mount, apply pressure only to the outer steel rim. Pressing on the rubber seal or the inner cage will instantly destroy it.