Inside -- Outside Calipers

Direct reading calipers allow for a quick visual check of measurements like the distance between a barrel channel and ramrod grove.

These are brass and date from the first half of 20th-century.

In the John Wyke of Liverpool tool catalog, from the third quarter of the 18th century, these are listed as being made of steel. He offered several sizes.

Cross section of a rifle forestock. The calipers could be used to quickly measure from the bottom flat to the outside of the stock. (top)