A Dobbie Key.
A Dobbie Key. Made from hollow Iron tube, solid Iron head. Size 16″ inches long. Head 2″ inches wide. Handle 1″ inch diameter.
This key was used to pump up the Hydraulic Dobbie Pit Props on the coal face by placing the key into the pumping valve on the side of the prop and move the key (left to right) to pump up the pressure to extend the prop piston. To release the prop piston you place the key hook into the valve and lever the opposite direction.