The Starrett 569M Tube Micrometer is used for measuring the wall thickness of tubing and other parts with cylindrical walls. Also for measuring from a hole to an edge (note minimum hole sizes in table). Rigid steel "half" frame with smooth black enamel finish. Anvil diameter = 0.185". 0-25mm Range, 0.01mm Grad, 4.8mm min. hole size, Plain, Carbide Spindle.