Guide-blocks for ends of crossheads, are easily gripped in a vice-chuck, in order to plane all those surfaces which are at right angles to the holes, or intended holes ; and the blocks may next be fixed on a table as shown in Fig. 741, the bottom edge of each block being adjusted to one of the long lines on the table-face, the line being denoted by L in the Figure. The blocks may be thus held by merely the plates which are shown in the Figure, if of gun-metal, but if steel blocks are to be planed, they require additional fastening by means of a couple of poppets being put to each block, one at each side.

Guide-blocks for standards, and for guide-portions which are solid with their framing, have usually flat surfaces for contact with the faces of the guide-slots; such surfaces belong to the blocks shown in the Figure (741) and their planing is effected with ordinary facing-tools. Guide-blocks for single guide-bars, are grooved, so that each bar can lie in its groove and be clasped by the block. The accurate planing of such is performed with corner tools, and the correct measurement, with coupled gauges, or as substitutes, with callipers only.