Forend screw

Double cylinder (right) and half cylinder (left) with forend screw to fix the lock cylinder

A forend screw (also cylinder locking screw ) is a screw with a metric thread and a countersunk head (Phillips, hexagon socket or Torx ), which locks the profile cylinder in the lock case and thus prevents the profile cylinder from being pulled out when installed. The forend screw is screwed in through the forend and is not accessible from the outside when the door is closed.