Construction: Aluminum carriage & base, hardened steel shafts and balls, or roller, mild steel end caps. Black Anodized. Specifications: Straight line accuracy (ball .0005"/inch of travel) (Roller .0001"/inch of travel) Coefficient: .003 typical. Repeatablility: (ball: .0002") (roller: .0001") Ball Slide - p/n ends in B Crossed Roller Slide - p/n ends in C