These are an indispensable addition to the turner's armoury for measuring both wall thickness and diameters. Because of their design the measurement taken at one end automatically transfers to the opposite end. This enables the turners to take an accurate measurement reading without the need to remove the callipers. Available in 4" and 7" models. The 7" version has an increased depth of throat at one end which permits the callipers to be used in large diameter vessels which have restricted openings.