This set of Plungers is designed to go with the Grandwork Underlevel. They come with three lengths in increments of 5/16" (approximately the height difference between bass strings and treble strings in an overstrung scale. For string leveling, choose the longer pair or the shorter pair and adjust the spring height screw from the underside of the Underlevel. Because the spring needs to be weak, the height difference between bass and treble will be faster to deal with using height-appropriate plungers.