Clark's expansion bit, Fig. 401, is designed to cut holes of varying size by means of a shifting cutter. It is made in 2 sizes, one ranging from 1/2 in. to 1 1/2 in., and costing 7s. 6c?., and the other embracing all diameters between 7/8 in. and 3 in., and costing 11s. One of these tools not only replaces a complete set of the ordinary kind, but enables holes to be bored of all intermediate sizes. These, however, are seldom required in the general way.