For the Dial Depth Gauges, 5 bases are available with the following dimensions: Base TB 50 50 x 16 mm Base TB 80 80 x 16 mm Base TB 100 100 x 16 mm Base TB 120 120 x 20 mm Base TB 150 150 x 20 mm The bases are interchangeable. Each base has a bore of 8 mm Ø H7. It is matt chromed and hardened. The contact face is lapped. The metal collet attachment guarantees reliable fixing of the Dial Gauges. Flatness according to DIN 876/0.