In carriages suspended from C springs, the front and hind wheels are connected by a central longitudinal timber, called a perch. This has to be plated with iron in order to prevent its breaking when running over bad ground; and without this precaution there is great danger of the perch giving way, as owing to its curved form, which follows the contour of the body, it is necessary to cut across the grain, and thus weaken the timber. These wooden perches have, to some extent, been superseded by wrought-iron perches, as previously mentioned, and these have been found to answer admirably. In C spring carriages there are the loops, which serve to suspend the body; and these require very good workmanship, for they are curved in many opposite directions, are tapered and irregularly formed every way, yet requiring to have bearing bolts accurately adjusted, and sundry contrivances for affixing ironwork to them, and all this without a single square side for the mechanic to work from. They are samples of great mechanical skill and dexterity of hand. Other carriage ironwork may be generally divided into stays, plates, hoops, clips, bolts, steps, treads, joints, shackles, and jacks. Stays are iron brackets of various forms, bolted by their extremities to such parts as they are intended to sustain or strengthen, but they do not take a bearing on any part. Plates are irons which take a bearing throughout their length and breadth on the part they are intended to strengthen, and to which they are fastened by bolts, screws, or rivets. Hoops are flat straps of iron riveted or welded together, for the purpose of securing timbers together side by side. Clips are a kind of open hoops, the ends of which have a thread run upon them in order to take nuts. The purposes for which they are used is to screw springs and axles in their places without having to weaken them by drilling holes through them. [Illustration: Fig. 32. AXLE CLIP CARRIAGE BOLT POINTED TIRE BOLT STEP BOLT ELLIPTIC HEAD PERCH BOLT =T= HEAD OR SHAFT BOLT CONE HEAD BOLT ] Bolts are cylindrical pieces of iron of various sizes (Fig. 32), one end of which is flattened out to form a head, and the other is formed into a screw to receive a nut. The use to which they are applied is to secure the ironwork and heavy framework. Steps may be single, double, or treble. In the two latter cases they are made to fold up, and are called folding steps, and may be made to fold up outside or into the body; this latter is the best way, and if they be well managed they do not incommode the sitters inside. Treads are small single steps a few inches square, fixed for the most part on a single iron stem. Joints are jointed iron stays, made in the form of the letter S, and serve to keep the leather heads or hoods of open carriages, such as landaus, stretched firmly out when required.