What tool would primarily be used to measure the distance between the jaws in a vise?

The tool primarily used to measure the distance between the jaws in a vise is calipers. Calipers are precision measuring instruments that can accurately ascertain the space between two points. They have two arms—one fixed and one movable—that allow for the measurement of internal and external dimensions as well as depths.

In the context of measuring the opening of a vise, calipers can provide precise readings of the distance between the jaws, ensuring accurate setups and adjustments for various tasks. The versatility of calipers makes them ideal for this purpose compared to other tools.

Other options, such as a bench vise and pipe vise, are tools designed for holding workpieces securely rather than measuring. Clamps are similar in that they are used for securing items but do not offer measurement capabilities. Therefore, the correct choice of calipers highlights their specific function in accurately gauging distances.