A Dowty Key.
Made from solid iron. Size 14 1/2″ inches long. The head is 2″ inches wide with the handle being 3/4″ of an inch diameter.
This key was used to pump up the hydraulic Dowty 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 downwards to pull the valve outwards.