Our Grey Door Silence is made of a heavy duty durable rubber material. They were invented as a solution for quieter doors. You affix them to the frame of a door and work well on both metal and wood doors. Silencers are installed by drilling a cavity into the stop strip of the door frame. The rod/cone portion of the device then slips inside the cavity. It can be secured by simply driving a brad through the stop strip and into the rubber stem of the device. The flat portion of the door silencer will lie slightly raised from the stop strip. The rubber acts as a shock absorber and is flexible enough for the door to close. 15 Door Silencers are included per package.