Understring radius gauges allow you to accurately set the bridge saddle height and radius without the string sizes distorting the measurements. The set of 9 is made up of all common radius measurements used, 7.25", 9.5", 10", 12", 14", 15", 16", 17" and 20".

The top and bottom edges are parallel so you can use the bottom edge to measure the fretboard radius or set the height of pickup pole pieces and the top to measure the strings by the bridge saddles.