E. Howard Watch Co. (Keystone) Series 10

The Series 10 was introduced c.1911 as a replacement for the Series 1 that had been in production since the Keystone Case Company began selling watches under the E. Howard brand. As the Series 1 was being transitioned out, several movements with the standard safety barrel were marked “No. 10.”
The Series 10 was constructed using the same 1907 Bridge Model as the Series 1 featuring a going barrel and friction plate jewels. The iconography of the star and arrow was retained on the center bridge, identical to the later Series 1 variations. In addition, the barrel bridge was marked “Series 10” adjacent to the crown wheel. The upper balance cap was fitted with screws from under the balance bridge, hiding the screw heads from view and providing another differentiation between the Series 1 and Series 10.
The movements were initially issued with a simple “Pat’d’” mark on the pillar plate with no year designation. After the first two runs, movements were marked “Pat’d ’10,” presumably once the U.S. Patent #978612 was approved for the escape wheel end stone cap in December 1910.
Earlier Series 10 variations contain a train constructed with brass while the later movements feature a white metal train. The transition to the white metal train is not sequential in relation to serial numbers.