Enamelled Frame . For the measurement of 3 or 5 fluted end mills, taps and reamers etc. Outside diameters can be directly read, or by applying the single wire method pitch diameters can be measured. Also used for checking out of roundness in centreless grinding operations. Positive locking clamp and constant force ratchet. Accuracy: Measuring Faces: 1-15mm /-4 mu m, 5-25mm /-4 mu m, 25-45mm /-5 mu m. Flatness: 0.3 mu m. Parallelism: (3L/75) mu m. L maximum measuring length. Measurement of Pitch Diameter: Pitch diameter E is given by the following formulae after taking the reading 'M' of micrometer by single wire method. 1. Whitworth (55) E (2M - D) - 3.16567d 0.96049P 2. Metric or unified (60) E (2M - D) - 3d 0.866023P. Where: M 1/2 (M'/0.4472 - 0.2361D). (5 flutes). E Pitch diameter. P Pitch of tap. D Diameter of tap. d diameter of wire. M' micrometer reading