An automatically engageable jaw clutch having a toothed drive hub, a toothed power take-off hub, and a clutch star axially displaceable with respect to the power take-off hub. The clutch star is continuously connected with the drive hub for conjoint rotation by means of first teeth means formed thereat and has second teeth means which can be brought into engagement with the teeth of the power take-off shaft by axial shifting of the clutch star. A screw socket or sleeve which is connected by means of a pair of coarse-pitch threading with the power take-off hub, is only conjointly axially displaceable together with the clutch star and rotatable relative thereto. The screw socket is entrainable by the clutch star by means of a pawl blocking mechanism composed of a pawl and ratchet teeth, when the drive hub overrides the power take-off hub. A switching device serves for selectively rendering ineffectual the pawls and contains a sleeve which is axially adjustable in relation to the clutch star and equipped with a ramp surface which, in a predetermined axial position of the sleeve in relation to the clutch star, hinders the pawls from engaging with the ratchet teeth.