The Mitutoyo 209 series internal measurement dial caliper gauge has a dial display and large measuring depth for taking inside dimension (ID) comparison measurements in standard inch units of hole diameters, thickness of grooves or tubes, and other hard-to-reach internal dimensions. They should be used with a setting ring or micrometer (sold separately).

Depending on the model, the caliper may come with ball contact points suitable for measuring external wall thickness of tubes, chisel contact points suitable for measuring flat surfaces, or an interchangeable set of contact points. The calipers’ jaws are spring loaded, which provide the point contacts with constant measuring pressure. The calipers have an Ingress Protection 65 (IP65) rating, which means that components are resistant to penetration by dust and debris, and resistant to penetration by liquids and coolant up to the force of a low-pressure (to 30 kilonewtons/meter-squared) water jet.

Calipers measure the distance between two opposing sides of an object. They make inside, outside, depth, or step measurements, according to their type. Calipers are commonly used in architecture, metalworking, mechanical engineering, and machining. The simplest calipers have two legs to mark the two points and require a ruler to take the measurement. More complex calipers use two sets of jaws instead of legs and have up to two graduated scales. Vernier, dial, and digital calipers give direct and accurate readings and are functionally identical, having a calibrated scale with a fixed jaw, and another jaw with a movable pointer that slides along the scale. The vernier caliper has a scale sliding parallel to the main scale for an additional, fractional reading to improve measurement precision. The dial caliper has a circular dial with a pointer on a toothed gear rack replacing the second vernier scale. As with the vernier, this second measurement is added to the reading from the main scale to obtain the result. The digital caliper takes a differential by zeroing the display at any point along the slide, with an LCD that displays a single value in English and/or metric units.

Mitutoyo manufactures precision measuring tools, metrology equipment, and systems. The company was founded in Tokyo in 1934 and formed Mitutoyo America Corporation in 1963, which is headquartered in Aurora, IL.