Abstract: There is disclosed a block piece for holding an optical workpiece, in particular a spectacle lens, for machining thereof, which block piece comprises a basic body which has an end face, against which the workpiece can be blocked by means of a temporarily deformable material, and a clamping face via which the workpiece blocked on the basic body can be fixed on a spindle of a machining machine. According to the invention, the basic body is injection-molded from plastic and is provided on its end face with at least two cut-outs for receiving the temporarily deformable material, said cut-outs being arranged on either side of an imaginary plane which contains the central axis of the basic body, and the boundary face of said cut-outs which is closest to the central axis of the basic body in each case forms an undercut.