Which of the following instrument is used to check concentricity of outside diameter?
Northern Coalfields Limited - 2020, NCL Technician - 2020,
Answer: C
Concentricity of an outside diameter is checked with a dial test indicator.
Concentricity is a check of runout: the work is rotated, between centres or on V-blocks, while the indicator's stylus rests on the diameter. Any eccentricity shows as a swing of the pointer, read directly in hundredths of a millimetre.
A vernier caliper, an outside micrometer and a dial caliper all measure the size of a diameter at one place. They cannot show whether that diameter runs true about the axis, which is what concentricity means.
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