Security screw
A security screw is a screw with a special screw head, so that the screw can only be loosened with a special, not commonly used tool or not at all.
| Typical screw head drives for security screws |
|
|---|---|
 |
Inside hexagon with pin |
 |
Torx with pin (Torx-TR) |
 |
Internal spline ( XZN ) |
 |
Disposable slot |
 |
Tri-wing |
 |
Torq set |
 |
Pentalobe |
 |
Stretcher |
 |
Bristol |
Simple security screws can be both tightened and loosened with special tools - for example with a special screwdriver or with special screw bits.
Disposable screws can only be tightened but not loosened with a normal screwdriver. The flanks of the slot are bevelled in the opposite direction so that the screwdriver cannot get a hold (one- way drive ). If loosening is required, special tools (e.g. a left-hand extractor ) must be used.
Screw head shapes
Safety screws have special screw head shapes, also known as screw head drives:
- Hexagon socket or Torx profile with center pin , so that only a screwdriver with a corresponding inner hole can be used; these screws can be opened after the pin breaks away
- Three-wing Phillips screws, where the wings point to the center (Y-Type) or do not meet in the center ( Tri-Wing )
- Four-wing Phillips screws with the wings of the cross not pointing towards the center ( Torq set )
- Flat slot with interruption or double hole head: the screwdriver blade must have a corresponding recess ("tensioner bit")
- Inside square ( Robertson screw ) and inside triangle, outside triangle (e.g. previously used in explosion-proof housings)
- One-way slotted: slotted screws with a beveled flank towards the direction of release
- Asymmetrical internal teeth, for which a suitable adapter is supplied. Use z. B. as theft protection for vehicle wheels ( wheel bolt locking ); Usually only one of the wheel bolts of a wheel is replaced by a locking screw
- Multiple heads in which several gaps are left out so that matching encoded keys are possible, used e.g. B. for luggage racks for car roofs
See also: List of screw head drives
Applications
Device manufacturers want to use security screws to make it more difficult for the user to open a device and under certain circumstances repair it himself or at risk instead of having it repaired by a professional or buying a new one. Examples are also children's toys with dangerous electrical voltages or substances inside.
In explosion-proof areas, safety screws are used on housings that contain possible ignition sources inside.
Security screws are still used to counteract unauthorized dismantling or theft, for example for screws in public transport, wheel screws for cars and screws for attaching the license plate.
Bits (screwdriver sockets) are available in retail outlets for almost all security screws that can in principle be removed .
Shear bolts
Shear bolts can be installed with standard tools, but the hexagonal part breaks off at a certain torque during installation. At the end of the assembly, the underlying round part of the screw head remains. However, this remaining part of the screw can no longer be loosened with a standard tool.