Abstract: This disclosure relates to an adaptor for a countersinking device and inces a pair of plates disposed in generally parallel relationship to each other and being relatively movable between minimum and maximum distances, the first plate carrying a countersinking tool, the second plate having an aperture in alignment with the countersinking tool, means normally urging the plates toward their relative position of maximum spacing, and adjustable stop means for limiting the relative movement of the plates toward their minimum position of relative spacing.