Made of Bearing Steel material, Double Side Rubber Seal Linear Motion Ball Bearing.Great for linear motion on 3D printer, cnc, and other applications.These ball bearing are fitted with two rubber dust sealed to prevent ingress of dirt, water and foreign matter.Bearings may require lubrication and break in period.Smooth moving, low friction, high rigidity and long life. Economical, easy to maintain replace.Product Name: Linear BearingMaterial: Bearing Steel, RubberColor: Silver ToneModel: LM12UUOutside Diameter: 22mm Inside Diameter: 12mm Length: 32mmWeight: 142gPackage Content: 4 pcs x Linear BearingOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.