Features: The shell is made of metal, durable for use. Standard processing makes the product has high interchangeability. The inside slide block is a high precision liner bear. Surface oxidation treatment, beautiful, and rust-proof. High accurate and stable performance. Specifications: Model: Size(Approx.) Installation Screw Size(not included) Weight SBR10UU 36 x 32mm / 1.4 x 1.3in M5 67g SBR12UU 39 x 40mm / 1.5 x 1.6in M5 93g SBR16UU 45 x 45mm / 1.8 x 1.8in M5 143g SBR20UU 50 x 48mm / 2.0 x 1.9in M6 185g Material: Metal Package List: 1 x Slide Block 1The shell is made of metal, durable for use. 2Standard processing makes the product has high interchangeability. 3The inside slide block is a high precision liner bear. 4Surface oxidation treatment, beautiful, and rust?proof. 5High accurate and stable performance.1 x Slide Block