The use of a cup-chuck for planing, is analagous to that of a vice, a cup-chuck being a sort of substitute for a vice, or for a vice-chuck. Either a vice, or a vice-chuck, will hold a cylindrical object above a planing-table, by means of vee-clamps, which were described in page 206; and a cup-chuck situated on a planing-table, also will grip a cylindrical piece, either with clamps or without them, because the points of the chuck-screws are made to bite the curved surface of the object being held. In Fig. 742, a cylindrical piece is shown gripped with the four screws belonging to the chuck, and a secure grip is thus obtained to plane the upper surface. A chuck of any special depth may be used to suit the lengths of the articles to be held; and for a deep chuck, four more fixing screws are required, which are situated at the bottom part of the cup-portion, near the planing-table.