In cases where it is inconvenient for the bolt head to pass through the work a T groove is employed, as in [Fig. 398]. In this case the bolt head may fit easily at a b to the sides a b of the groove, so that while the bolt head will slide freely along the groove, the head, being square, cannot turn in the slot when the nut is screwed home. This, however, is more efficiently attained when there is a square part beneath the bolt head, as in [Fig. 399], the square a of the bolt fitting easily to the slot b of the groove.
Fig. 400.
Fig. 401.
Fig. 402.