When the door casing is less than \ inch thick the base does not finish well against it, and a " plinth block " should be placed at the bottom of the casing, as shown at A, Fig. 234, and also in Fig. 268. This block should be about ¼ inch higher than the base and at least \ of an inch thicker than the base or casing. With pilaster casings the plinth usually has a plain rectangular section, but with mitred casings the plinth has a section corresponding in outline with that of the casing, as shown at P, detail F, Fig. 234, and also in Fig. 235. With 1 1/8-inch casings or back bands, and a 7/8 inch base, plinths are not necessary and are often omitted, even in the best work, according to the taste of the architect. Aside from stopping the base, however, the use of a plinth block avoids carrying the more delicate mouldings of the casing to the floor, where they are apt to become filled with dirt.