The Starrett PT26431 adjustable jaw accessory for 120-series dial calipers measures different planes that cannot be reached with a standard caliper. The adjustable reference jaw is 3-1/2” long and can be made either longer or shorter than the sliding jaw. Jaw extends up to 5/8” longer than the sliding jaw and is made of hardened stainless steel for durability and long life.
Calipers are used to measure diameter and depth or to replicate a measurement from one space to another. Calipers feature a main scale of measurement, a secondary scale of measurement, inner jaws to measure internal diameter, outer jaws to measure external diameter, a locking screw to hold the jaws in place, and, in most cases, a depth probe. Vernier calipers are the most commonly used, because the vernier scale is so precise that it measures the points between the marks on a standard inch or metric scale. For example, if the primary scale has markings for every 10th of an inch, the vernier scale has markings to measure 1/1000th of an inch. While calipers are suitable for measuring items with consistent thickness, a micrometer may be necessary if the item has a lip, rim, or bevel on the edge.
The L. S. Starrett Company was founded in 1880, originally manufacturing bench vises, squares, and other tools. They acquired other companies throughout the years, expanding their services into making precision measurement instruments and tools, such as calipers, micrometers, saw blades, and gauges. Starrett is headquartered in Athol, Massachusetts and has manufacturing facilities in Brazil, the United Kingdom, China, and other locations.