The keys are generally made of hard wood, sometimes compressed by a special process, cut slightly taper, or wedge, shape, and driven in between the jaw of the chair and the vertical web of the rail. On some railways the key is placed outside the rail, as in Fig. 297, and on others inside the rail, as in Fig. 298. The latter method possesses many advantages over the former. The outer jaw of the chair can be brought well up to the under side of head of rail, giving the rail more lateral support and better means of preserving the correct cant; and, as in this chair the outer jaw permanently fixes the gauge, the working out of one or more of the keys does not leave the rail exposed to be forced outwards and widen the gauge, as in the case with dropped keys in outside keying. Another and very important advantage of inside keying is that platelayers, when inspecting the road by walking between the rails, can readily examine the keys on both sides. [Illustration: Fig. 292, 293, 294, 295, 296, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306] Chairs have been made, as in Fig. 299, with a recess in the rail-seat, 209 to hold a piece of prepared wood, or other suitable semi-elastic material, the object being to provide a rest, or cushion, softer and more yielding than the cast-iron. The idea looks well in theory, but in practice the pounding on the rail compresses or crushes the wood lower and lower into the recess, slackened keys have to be tightened, and when the wood has been worn or crushed away down to the level of the stop ribs, A, A, the under side of rail has no longer any seat, or rest, beyond the two narrow ribs of cast-iron. These afford such a very limited support that the rail becomes notched, and produces a very rough clattering road. It is a very simple matter to take out an old key and put in a new one, but to replace a wooden cushion in a chair recess involves the entire removal of either the rail or the chair. Chairs with wooden cushions have not been adopted to any great extent, the tendency of modern practice being to reduce as far as possible the number of parts of the permanent way, and to provide those parts with ample bearing or contact surfaces.