The Robert Sorby Threading & Sizing Gauge is ideal for box-makers.
This gauge takes all the guess-work out of fitting the major and minor diameters of pieces. With the gauge set at the unmarked anvil this creates a 1:1 correlation between the measuring faces and facilitates accurate push fits.
The other three anvils are marked 10,16 and 20 which relates to the tip most commonly used by thread cutters. The gauge has a built-in compensation factor to ensure a perfect thread between internal and external diameters every time.