The invention relates to a lock for releasable locking of an excavating tooth to a wearing-part holder in a wearing-part system, where the excavating tooth and the wearing-part holder together define a lock opening for receiving the lock, where the lock comprises a threaded conical screw and a first thread half designed with a first thread bed, where the first thread half and a second thread half, designed with a second thread bed, are mounted in the lock opening, where the first thread half and the second thread half, with the thread beds directed towards each other, together define an opening for threaded fastening of the threaded conical screw, such that rotation of the threaded screw moves the threaded screw along the thread beds in the axial direction of the screw into the lock opening, locking the lock when the first thread half is moved towards the excavating tooth and the second thread half is moved towards the wearing-part holder. The invention also relates to a wearing-part system, a first thread half, a second thread half, a conical screw, and an associated method for releasable locking of an excavating tooth to a wearing-part holder in a wearing-part system with lock.