=33. Strap and Corner Hinge Plates.=—Medieval hardware was the product of the blacksmith and the whitesmith, the former working with forge and hammer, and the latter with chisel and file, the material being wrought iron. The butt hinge was unknown, while the strap, or surface, hinge was in universal use; and, as this was wholly in sight, it naturally became the subject of decoration, chiefly in outline, but occasionally in surface ornament also. With the adoption of the butt hinge for general use, the opportunity of utilizing the hinge to decorate the surface of the door disappeared, but with the modern revival of decorative art the use of constructive metal work as a feature of surface decoration for important doors was restored. This was accomplished by combining with the modern butt a surface plate that represents the strap hinge. Obviously, the width of the butt of a hinge plate should correspond with the height of the butt hinge with which it is to be used, and both should be of the same metal and finish. The other dimensions are governed by the size of the door and by taste, as is true also in the case of corner plates. A varied and artistic selection of typical strap hinges and corner plates is given in the groups of designs shown in Figs. 34 and 35. LOCKS AND THEIR APPURTENANCES =34. Locks in General.=—In no other line of hardware is there such a variety of grades and types as there is in door locks. In general, locks may be designated as _surface_ and _mortise locks_, the former being secured to the surface of the door and entirely exposed to view, while the latter are let into a mortise cut in the edge of the stile. Besides these two general kinds of locks, there are several special locks, which will be fully explained. As to quality, locks may be classified in three grades; namely, _common_, _medium_, and _high grade_. [Illustration: FIG. 36] [Illustration: FIG. 37] =35. Common-Grade Rim and Mortise Locks.= The =rim lock=, as illustrated in Fig. 36, is generally used for buildings of the cheapest class, such as tenements and small houses. As cheapness is the controlling factor in such goods, especially the goods made for speculative building purposes, the quality diminishes with the price. For cheap work, rim locks are used on account of their low cost and because they are easily applied. They also require no trim, such as escutcheon plates, etc., and are complete when the spindle and the knob are furnished with them. Rim locks are made in various sizes and either square or rectangular in shape, the long dimension being placed either horizontal or upright. They may also be obtained with either iron or brass bolts, and are furnished with iron, tinned, or nickel-plated keys. The cheapest grades of rim locks are made with two bolts and one tumbler, while the better grades have an additional stop and a slide bolt with three tumblers.