The thin 0.79” diameter measuring discs, with 0.030” edge thickness, enter narrow grooves, slots and recesses, to take measurements on work sections such as ribs, lands, fins, cutting edges on form tools and chordal thickness on gear teeth.The thin 0.79” diameter measuring discs, with 0.030” edge thickness, enter narrow grooves, slots and recesses, to take measurements on work sections such as ribs, lands, fins, cutting edges on form tools and chordal thickness on gear teeth