Plates for holding or gripping the pieces of work, are always used in conjunction with bolts and nuts, the bolts being put through the holes or slots in the plates. A middle plate is one denoted by Fig. 638, or by 640, and is used when the bolt or bolts must be between two portions of the article to be gripped. An end plate is shown by Fig. 639, and is required when the part to be gripped is to be between the two screw-bolts, one at each end of the plate. An edge plate is represented by Fig. 641, and is principally used in contact with edges of various pieces of work when bolts cannot be applied near the centre parts. A U-plate is a very useful tool, and is made by bending a piece of bar iron or steel to the form of a letter U ; a plate of this class is shown by Fig. 642, and will admit a bolt at any place along the gap that may be requisite to suit a certain slot in the table. A slot plate denoted by Fig. 643, is rather more efficient than a U-plate, because neither end of a slot plate can spread open while tightening the bolt, which always results to some extent, with a U-plate. A slot plate is, however, more difficult to make, through the necessity for punching or drilling the long slot. A U-plate is remarkably useful in cases of emergency, because it can be made by a skilful man in two heats, if the bar used is not more than one inch thick. Figs. 644 and 645, represent bolts and plates together in their relative positions for use. By observing the ends of the plates in these Figures, it will be seen that they are thinner than the intermediate portions; this should be their shape for two purposes, to make the plate relatively strong at the hole, which is where the plate is liable to break, and to prevent the end of the plate projecting much above the work after being fixed. These thin ends, and all other ends of plates which grip or bear upon the work, are the paws of the plates. A cap plate indicated in Fig. 646, is not for general work, but is remarkably efficient for effecting a firm grip, and is a sort of superior end plate (Fig. 639). Cap plates are used for fastening long pieces of work that are comparatively narrow, such as. spindles, rods, bars, shafts, and axles.