The side plates are each provided with a hole to receive the barrel trunnions, and in the case of the ·303-in. gun, with hooks for engaging the recesses on the top of the barrel block; also guides in which the flanges of the lock move, which are enlarged at the rear end to act as crank stops; in addition each has a bearing, through which the crank passes, thus connecting the latter with the barrel; these bearings move in slots in the breech casing. The left side plate is fitted with a connecting rod spring to hold the connecting rod upright when the lock is removed, and the right side plate is fitted with a side plate spring near the barrel, to keep the extractor in its highest position when the lock is home. The left side plate is prolonged to the front, and has a recess in which the bottom lever of the feed block engages. The crank is fitted with a connecting rod, which is free to rotate on the crank pin, and, outside the breech casing on the right, with a handle which has a curved projecting arm, and on the left with a fusee, to which is attached a chain. The connecting rod is attached to the crank by means of an axis pin, called the crank pin, and is arranged to take the lock by means of an interrupted screw, thereby connecting the crank and the lock. The connecting rod is divided into two parts, enabling its length to be increased by inserting washers of varying thicknesses. By this means it is ensured that a firm pressure is kept on the base of the cartridge at the moment of firing, thus preventing separations. On the left of the breech casing there is a strong spiral spring, called the fusee spring, the rear end of which is connected by the fusee chain and fusee with the crank; the front end is attached to the breech casing by means of the fusee spring box and adjusting screw, which passes through the front end of the fusee spring box, and through the nut at the front end of the spring. The lock is attached to the connecting rod by the screwed head, and when in the firing position closes the breech. In this position it is held by the side levers, the crank (which bears against stops on the side plates), and the connecting rod, the joint being slightly above the horizontal, to prevent the breech being opened at the moment of firing. The lock has a reciprocating motion communicated to it by the rotation of the crank, and is kept in position during its backward and forward movements by means of flanges working in guides on the side plates, and, when at the end of its backward travel and clear of the guides, by the gunmetal block underneath the cover.