This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
Not infrequently it is desired to know the distance from one side to another of some part that cannot be directly measured with a rule, and when no calipers are at hand. But with a vise handy, the measurement can be made with ease and with sufficient accuracy for all practical purposes if the vise is not too worn. This trick is particularly adapted for cali-pering threaded parts, as threads cannot be measured readily with ordinary calipers. How this may be done is shown in the sketch, which illustrates the method as applied to a screw. The work is gripped between the jaws of the vise and the opening then measured with a rule. - Contributed by Donald A. Hampson, Middletown, New York.
Ill: The Jaws of a Vise, If They Are True, Will Make a Caliper Gauge Giving a Perfect Measurement