The Starrett 123-12 master vernier caliper measures 0 to 12 inches with 0.001” accuracy, and comes with a mail-in card to request the standard letter of certification (SLC). Once the card has been mailed in, Starrett sends the SLC with caliper model and serial numbers, ensuring that the exact caliper purchased has met National Institute of Standards and Technology master standards. The vernier scales are longer than normal, with 50 divisions, allowing half as many bar graduations as conventional single-vernier tools. These widely-spaced graduations make it easier to read a measurement from the caliper. This easy-reading measuring tool allows for reliable and accurate readings with the sharp, black graduations on the no-glare, satin chrome-finished bar.
The open-face design of the slide allows both the inside and outside vernier scales to be indicated on the same side, allowing both inside and outside measurements to be read without turning the tool over. The screw-type adjusting nut allows for fine measurement adjustments for accuracy, while the lock nut holds measurements for reading, repeating, or transferring the measurement. The tool steel construction makes the jaws harder and more wear-resistant than an equivalent stainless steel jaw. The bars are hardened and stabilized. The measuring surfaces are hardened, ground, and lapped, for a very hard, flat, and polished measuring surface that is considerably more accurate than a surface that has not had these operations performed. The graduations on the bar are machine-divided for accuracy. The master bar’s combination of straight and angular ways allow positive alignment of graduations, and easy adjustment of the flush-fitting verniers. Aligning flush vernier plate graduations to the same plane as the graduations on the bar ensures readability and accuracy. This caliper has divider points on the back side to help accurately set dividers and machine parts. This caliper has inch and millimeter graduations on the same bar, so outside measurements can be taken easily, while inside measurements must be compensated for by adding the nib width to the indicated reading. The maximum closed nib width of this caliper is 0.300”. The bar width on this caliper is 15/16”. The jaw depth is approximately 2-5/16”. The longer length of the adjusting jaw slide provides a longer bearing surface on the master bar, which ensures that the bar and solid jaw are square. This longer bearing surface also means the caliper has additional stiffness for resistance to springing and therefore, more accurate measurements. Tight, smoothly fitted slides offer a high level of accuracy along with easy adjustment.
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, machining, manufacturing, carpentry, and medicine. 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 dial caliper is used also for measuring size differential between two objects. The digital caliper takes the same sort of differential measurements as the dial caliper by zeroing the display at any point along the slide, with an LCD (replacing the dial) that displays a single, easily read value in both English and metric units. Some digital calipers can hold data readings between measurements and send them to data collection devices.
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.