Abstract: An improved method and apparatus for blocking semifinished lenses by the adjustment of each such lens until it occupies a prescribed position where an alloy hub or "block" is removable affixed to the lens by an adhesive pad so that the lens can be held for finishing, is characterized by magnetically securing the block to a chuck for carrying and affixing the block to the lens. The block may quickly and simply be secured to the chuck merely by being extended therein without the need for any mechanical devices, and upon being affixed to the lens is readily separable from the chuck upon withdrawal of the chuck therefrom.