310. U.S. Spring Scale. Pocket size, 4-3/4" long. Stamped flat metal. Horizontal beam with cut-out leaf spring hangs from hand-held upright. Slotted end of spring holds vertical arm with hanging letter clip. Arm calibrated (0-4 oz.) and bears postage rates. Scale folds flat to fit in carrying case. Markings: "Pat. Pend. Postage Saver Scale."