Polished Brass. Perkomatic® offers the ultimate in uncontrolled concealed door closing devices, with outstanding performance and excellent durability. Housed in a lightweight aluminium casing, the hydraulic mechanism can be easily adjusted to provide the desired latching action for each application, whilst the precision engineered chain ensures smooth and lasting service. Supplied with fixing screws and full fitting instructions.. Concealed - enhanced aesthetics - reduced opportunity for vandalism. Smooth controlled closing mechanism with latching action. Tested to withstand 500,000 open and close cycles. Suitable for use on light or medium weight internal doors