Where additional security is required for external doors opening outwards, hinges are usually supplied with integral security studs. Please see page 116 for hinges with security studs for use on new build projects. The security studs help prevent forced entry by stopping doors being levered out of frames even if the hinge pins have been driven out. Where doors have already been fitted with standard hinges without security studs, it is possible to fit independent hinge bolts - these are sometimes referred to as "dog bolts". These are designed for use on timber doors, but can also be used on steel doors. However, on steel doors it will be necessary to weld the hinge bolts in place. The hinge bolts should be fitted 75mm below the top hinge and 75mm above the bottom hinge. The bolts should be fitted in the door and the receiver plates fitted to the frame. They are manufactured from mild steel which is then bright zinc plated. They are supplied in pairs with two hinge bolts and two receiver plates packed together with screws for timber doors.