Close-up of a micrometre thimble scale. The circumferential, or thimble scale, of the metric micrometre is separated into 50 equal divisions each of 0.01 millimetres (mm). The thimble reading has to be added to the reading on the barrel of the micrometre to get the measured dimension. On this photograph the thimble measurement is 46 x 0.01 = 0.46 mm.