Made of Carbon steel+rubber material, Double Side Rubber Seal Linear Motion Ball Bushing. Great for linear motion on 3D printer, cnc, and other applications. These ball are fitted with two rubber dust sealed to prevent ingress of dirt, water and foreign matter. Bearings may require lubrication and in period. moving, low friction, high rigidity and . Economical, easy to maintain replace. Product Name: Linear Material: Carbon steel+rubber Color: Silver Tone Weight: 56g Model: LM8UU Outside Diameter: 15mm Inside Diameter: 8mm Length: 24mm Package Content: 4pcs x Linear Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the a little different from the real thing. The measurement allowed error is +/- 1-3cm.