Fig. 380.
Another method of securing a foundation bolt head within a stone block is shown in [Fig. 379]; a similar coned hole is cut in the block, and besides the bolt head b a block w is inserted, the faces of the block and bolt being taper to fit to a taper key k, so that driving k locks both the bolt and the block in the stone. When the bolt can pass entirely through the foundation (as when the latter is brickwork) it is formed as in [Fig. 380], in which b is a bolt threaded to receive a nut at the top. At the bottom it has a keyway for a key k, which abuts against the plate p. To prevent the key from slackening and coming out, it has a recess as shown in the figure at the sectional view of the bolt on the right of the illustration, the recess fitting down into the end of the keyway as shown.
Fig. 381.
Another method is to give the bolt head the form at b in [Fig. 381], and to cast a plate with a rectangular slot through, and with two lugs a c. The plate is bricked in and a hole large enough to pass the bolt head through is left in the brickwork. The bolt head is passed down through the brickwork in the position shown at the top, and when it has passed through the slot in the plate it is given a quarter turn, and then occupies the position shown in the lower view, the lugs a c preventing it from turning when the nut is screwed home. The objection to this is that the hole through the brickwork must be large enough to admit the bolt head. Obviously the bolt may have a solid square head, and a square shoulder fitting into a square hole in the plate, the whole being bricked in.
