A block piece for holding an optical lens to be machined, with a coupling part for being held in a workpiece chuck and with a holding part for fastening the lens. The holding part has a convex or concave holding surface corresponding to a first side of the lens. The holding surface is, according to the shape of the lens to be held, provided in the form of a negative free-forming surface, and the block piece is made from a plastic that can be machined. The principal axis of the holding surface is arranged set off and/or tilted relative to the axis of rotation of the coupling part