One-Way Machine Screws
One-way screws are special screws that can only be turned in one direction. They can be installed with a standard flat-blade screwdriver. One-way screws are commonly used in commercial restroom fixtures and on vehicle registration plates, to prevent vandals from tampering with them. One-way screws are only practical when the need for removal is unlikely. They are difficult to remove with conventional tools because the slot is designed to cause cam out when even minimal torque is applied in the direction to unscrew it. Instead, a special removal tool (a one-way screw extractor) must be used. Alternatively, a one-way screw can be removed by using a drill bit, by using a rotary tool and cutting disk to extend the slot, by using locking pliers, or by drilling two holes in the slot and removing the screw with a pin spanner (snake-eyes driver).