The gauge tailored for quick and accurate measurement of the fretboard base radius, without necessary removal of the strings. Laser cut from 1 mm stainless steel, the set of 4 gauges can measure radii 7.25", 9.5", 10", 12", 14", 15", 16" and 20". The two ones with narrow notches for use closer to the nut, the wider notched ones for use around the 12th fret.