=The Double-screw Elevating Device=, Fig. 60_a_, is used on 25 of the carriages for 3.6-inch guns. It consists of a hollow exterior screw (_a_) (having an exterior right-hand thread and an interior left-hand one) in which works an interior screw (_c_) to whose trunnioned head is attached the guide-strap (_s_), the arms of the strap being secured by nuts to the prolongations of the upper bolts that secure the middle transom. This insures rotation of the elevating device in a plane passing through the axis of the carriage. The bronze nut (_b_) in which _a_ works is arranged on trunnions between the cheeks of the carriage, and has the hand-wheel (_d_) (or in some cases a large gear-wheel) so fixed to it that the latter can be rotated but has no motion of translation. A groove (_e_) is cut on the screw _a_, and a key on the hand-wheel fits this. [Illustration: FIG. 60_a_.] Where the large gear-wheel is used motion is obtained by a small gear-wheel, axle, pinion, and hand-crank on the right of the trail. DESCRIPTION OF CARRIAGE FOR 3.2-INCH GUN. The carriage is made of steel. Its track, like that of the other vehicles, is 60 inches. The principal parts are the two flasks, connected by transoms, and the lunette; the two axle-plates, upper and lower; the axle-tree; the wheel-brakes; the wheels; the elevating apparatus; and the two seats. Each flask is formed by riveting together two plates with curved margins; and the trunnion-beds are reinforced by bars of steel, which are enclosed between the margins of the flask-plates and riveted to them. There are three front transoms, upper, lower, and rear, in the vicinity of the trunnion-beds and axle-plates, and three trail-transoms at intervals between these plates and the lunette, the latter being riveted on. Trail-handles are on either side of the trail near the lunette. The lunette, lunette-plate and trail-plate are formed of one piece of metal. The axle-plates, two in number, which accurately envelop the solid steel axle, are riveted together. The shoulder-washers are octagonal in form; to each is fitted a collar containing a stout eye, to which the brakes are attached. These collars have projections that embrace the axle-plates above and below to prevent turning of the axle within the plates. Linch-washers have a stud to keep them from revolving with the wheel. =Double-bow Spring-brakes=, with a device for detaching them when necessary, are used. They are carried in a vertical position by means of the button on the lever and the groove on under side of axle-seat guard-rail. The spring-lever operates the locking-bolt in the end of the brake near the hook, so that the brake may be available in going up or down hill. =Axle-seats= are placed on either side of the carriage. Underneath the left seat a section of picket-rope is carried.