=20. Strap Hinges.=—The common wrought hinges used to apply on the surface, for hanging doors, etc., and generally used in connection with rough work, such as bins, sheds, barns, etc., where a strong, serviceable hinge that may be easily applied is required, are known as =strap hinges=. They are constructed of wrought metal of various weights, according to the size of the hinge, and are stamped or cut from sheet metal, with _knuckles_, or sockets for the pins, formed on the strap; the pins passing through the knuckles are well riveted. There are two kinds of strap hinges; namely, _light-strap_ and _heavy-strap hinges_. The =light-strap hinge=, which is shown in Fig. 12 (_a_), is so termed because of its light construction and narrow joint. This hinge is made in inch sizes, varying from 3 to 16 inches in length. By inch size is meant the longest dimension when the hinge is closed; thus, a 6-inch strap hinge is 12 inches long from end to end when opened. They are listed and sold by the pair. [Illustration: FIG. 12] The =heavy-strap hinge=, which is shown at (_b_), is similar to the light hinge, but is made from heavier metal and has large dimensions at the joints, or knuckles. This type of hinge is used where a strong, substantial hinge is required. The heavy-strap hinge is made in inch sizes, from 4 to 16 inches in length. The 4- and 5-inch sizes are listed and sold by the pair, the 6-inch and larger sizes being listed and sold by the pound; the larger the hinge the lower the price per pound. As shown at (_c_), the heavy-strap hinges are also made with corrugated knuckles, which give additional strength where the construction is weakest. These are termed =corrugated-strap hinges=. All of the hinges described are also made in plain steel, japanned or galvanized, and may have brass pins or rivets. =21. T Hinges.=—As will be seen from Fig. 13, =T hinges= are so called to distinguish them from the strap hinge, as well as because of their construction, which is in the form of the letter =T=. The =T= hinge is used for practically the same purpose as the strap hinge, but is superior to it in strength, from the fact that its knuckle is wider than that of the strap hinge. =T= hinges are made in light, heavy, and extra-heavy grades, the former and latter types being shown in Fig. 13 (_a_) and (_b_). In arranging the sizes of =T= hinges, the measurements are given for the length of the strap only; the leaf of the hinge forming the =T= with the strap is not considered. Thus, a 6-inch =T= hinge measures 6 inches from the pin to the end of the strap leaf. =T= hinges may also be obtained in stamped metal, with corrugations, as shown at (_c_). These hinges can be had in all finishes. The light and heavy grades, as well as the 4- and 5-inch extra-heavy grades, are sold by the pair, while the larger sizes of extra heavy are sold by weight. [Illustration: FIG. 13]