Starrett 64445 Mechanical Micrometer Heads; Accuracy: 0.0020 mm; Thimble Diameter (Decimal Inch): 0.4063; Thimble Diameter (mm): 10.32; Digital Counter: No; Spindle Diameter (mm): 3.51; Spindle Length (mm): 9.53; Spindle Length (Decimal Inch): 0.3750