Every person operating a plant where machinery is used, shall provide such guards, boxing, screens or other appliances as will protect employees against injury from belting, shafting, gearing, elevators, drums, saws, cogs, electric currents, molten metal or hot liquid. He shall also furnish and supply belt shifters which can be operated from the floor. All exposed cogs or gears shall be enclosed in metal casings or woven wire screens. Protruding set screws in collars and couplings of shafting or other revolving machinery shall be countersunk or covered with metal boxing. Pulleys, belts and projections of or from ends of shaftings shall be protected by boxing or enclosing with metal or other suitable material. Belts shall not rest on shafting in motion, but rest hooks shall be provided to hold belting free therefrom. Roll guards shall be placed on roll-feed machines fed by hand at the point where the material is fed, and a device for instantly stopping the machine by the hand or foot shall also be provided within reach of the operator when operating the machine.