Selecting a Dial Caliper on Amazon.com
A dial caliper is a type of slide caliper with a graduated scale and a dial indicator for precise measurements of the inside and outside dimensions of an object as well as the depth of a hole. It is used in metalworking, mechanical engineering, machining, carpentry, and medical applications. Dial calipers have a pair of jaws attached to a beam that is marked with a scale. One jaw is fixed, while the other slides along the beam to accommodate the object being measured. The dial indicator is fixed to the movable jaw on a toothed gear rack that transfers the movement to the dial needle. To enable comparative measurements and documentation of readings, many dial calipers have a locking mechanism to hold the jaws in place. A depth rod extends from the beam to take depth measurements. For improved accuracy of depth measurements, particularly for wide holes, a depth measuring base, or foot, may be added to the beam.
Dial caliper measurements are read by combining the base measurement indicated on the beam with the final fraction of an inch or millimeter shown on the dial. A dial caliper may provide metric, inch, or both metric and inch readings. Depending on the level of precision required, a dial caliper may be selected for a particular accuracy or resolution. Most dial calipers measure to thousandths of an inch or hundredths of a millimeter. The maximum measurement varies from tool to tool, with a 6" dial caliper being a common size. A dial caliper may include a National Institute of Standards and Technology (NIST) traceable calibration certificate.
Certain dial calipers have offset jaws, with the different jaw lengths allowing measurement of stepped surfaces. A dial caliper may alternately have pointed jaws for measuring uneven surfaces, or blade jaws for measuring narrow grooves and recesses. Dial faces for dial calipers, such as a Mitutoyo or Starrett dial caliper, are available in different colors; a white face usually has an inch scale and a yellow face a metric scale, while a black or red dial face has white numbers for high contrast readings.