Fine American gilt Ball model railroad watch Circa 1920-1940

Gilt American railroad watch by Hamilton Watch Co.
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A fine American gilt railroad watch. Ball Watch Co. model Grade 999, Official RR Standard by Hamilton Watch Co., circa 1920-1940. 23 Jewel movement, jewels in settings, concentric damascened divided ¾ plate, bimetallic balance, overcoiled spring, swan’s neck regulator, stem wound, lever set. White enamel dial, black Arabic numerals, subsidiary seconds and blued hands. 10 Carat gold filled, Ball model, open face case by Keystone Watch Co., with stirrup bow.
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Diameter: 51 mm
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Signed: Trade Mark Official RR Standard Ball Watch Co. Cleveland – Ball Watch Co. Cleveland, O.