strong plates of iron which come over the trunnions of a gun, and keep it in the carriage. They are fastened by a hinge to the prize-plate, that they may lift up and down, and form a part of an arch in the middle to receive a third part of the thickness of the trunnions; for two thirds are let into the carriage, and the other end is fastened by two iron wedges called the fores-locks and keys.