The attachment-socket has a rectangular longitudinal mortice in which the tang of the clevis is placed. This tang has a slot, the lower part of which ends in a hole having the same diameter as the locking-bolt. The locking-bolt has bearings on each side of the mortice, and the part in the slot has two opposite rectangular grooves. When the bolt is in the hole with these grooves perpendicular to the slot, the clevis is locked; but when turned until the bottoms of the cuts are in prolongation of the slot sides, the tang of the clevis can be drawn out until stopped by the other end of the slot. =The Elevating Device= (4), Fig. 60, consists of _frame_ and _double lazy-tongs_. _The Frame_ consists of (2) side-levers (_c_), pivot-bolt and separator (_d_), transom-bolt and nuts in rear, (2) eye-bolts, elevating-screw (_f_), cross-head elevating-screw nut, crank-handle (_g_). _The Lazy-tongs_ consists of (4) long arms (_a_), (4) lever-arms (_a_), (4) short arms (_a_), upper assembling-bolt, (2) assembling-bolts, short, (2) assembling-bolts, long, central journal-bolt (_e_), lower journal-rod (_b_) and (2) bearing-boxes, (2) eye-washers (for strap _k_), and the necessary nuts and washers. The front end of the frame is attached to the carriage axle-plates, just in rear of the middle transom, by two eye-bolts which form the pivot. [Illustration: FIG. 60.] The rear end is attached to the elevating-screw by the cross-head elevating-screw nut, which moves back and forth in the grooves in the side-levers in rear of the transom-bolt. The crank-handle on the elevating-screw is located just in front of the trail-box. The double lazy-tongs (of two cells, the upper twice the size of the lower) are enclosed in the frame which furnishes bearings, at about the middle of the side-levers, for the central journal-bolt. The lower journal-rod has fixed bearings in the two bearing-boxes which are bolted to the flasks of the carriage. The gun rests on the upper assembling-bolt, which has eye-washers for the breech-strap. Any motion of the elevating-screw handle raises or lowers the frame, and this, carrying with it the central journal-bolt, opens out or closes the lazy-tongs cells.