What is a security screw, and how do I undo one without the right bit?
The common tamper-resistant drives, how to identify what you are looking at, and the methods that work when you do not have the matching bit.
- Difficulty
- intermediate
- Time
- 25 min
- Read
- 3 min
- Safety
- caution
Short answer
Identify the drive first: pin-Torx and pin-hex have a pin in the middle and are defeated by a security bit set, which is cheap and universal. One-way, clutch head and shear nuts cannot be undone by design and need gripping, slotting or drilling out. Buying the bit set is almost always faster than any workaround.
Security screws are designed to be a nuisance rather than an impossibility, and they fall into two groups: drives you cannot turn without the right tool, and drives that are engineered so they physically cannot be turned anticlockwise at all. Working out which group you are in tells you immediately whether you need a bit or a method.
Safety
Security fixings are often there for a reason — on electrical enclosures, meter covers, communal doors, playground equipment and rented property. Removing one on equipment you do not own or on a sealed utility enclosure may be an offence as well as dangerous. Never open a sealed electricity meter or a service head under any circumstances; that is the supplier's equipment and it is live.
What you'll need
- A security bit set (optional)
- Locking pliers (optional)
- A rotary tool with a thin cutting disc (optional)
- Eye protection
- Two-part epoxy or a spare nut, for the last-resort method (optional)
Step by step
- Identify the drive before doing anything.Pin-Torx and pin-hex look like ordinary Torx or hex with a raised pin in the centre. Tri-wing and Torq-set are aircraft and electronics patterns. Clutch head looks like a bow tie. One-way looks like a slot with one side of each wing ramped away.
- Buy the bit if it is a pin drive.A security bit set covers pin-Torx, pin-hex, tri-wing, spanner (snake eye) and clutch types and costs very little. This is the answer for almost every domestic case.
- Drill the pin out if you have the ordinary bit but not the security one.For pin-Torx and pin-hex, drilling the central pin away with a small HSS bit lets an ordinary Torx or hex bit engage. Go slowly, centred, and only deep enough to remove the pin.
- Grip the head from outside for a one-way screw.A one-way slot ramps a driver out anticlockwise but the head itself can still be turned. Locking pliers on the head, if it is proud enough, undo it directly.
- Cut a slot if the head is flush.A thin cutting disc in a rotary tool across the head gives you a flat-blade slot. Cut it deep enough that a driver does not simply burr the edges over.
- Use a shear nut's own design against it.A shear bolt has a head engineered to snap off at a set torque, leaving a smooth cone. There is no way to turn what is left — it has to be gripped hard with pipe grips, or drilled out.
- Epoxy a nut on as a last resort.Degrease the head, epoxy a nut squarely onto it, let it cure fully overnight, then turn the nut with a spanner. It works surprisingly often on flush heads and it is entirely non-destructive if it fails.
- Drill it out if nothing else works.Drill down the centre until the head separates from the shank, remove the item, then wind the exposed shank out with grips.
Tips
- If you are fitting security screws yourself, keep a driver bit taped inside the item. The person who has to open it in ten years is very often you.
- Clutch-head screws — the bow-tie pattern — will tighten with an ordinary flat blade but not loosen with one, which is exactly what they were designed for in old vehicles and coin-operated machines.
- For anything you may need to service, a pin-Torx is a far better choice than a one-way screw. It resists casual interference without making the job impossible.
Common mistakes
- Attacking a one-way screw with a flat driver — The ramped slot is shaped to push the blade out. All you achieve is burring the head so that grips will not hold it either.
- Removing security fixings from utility equipment — Meter and service head seals are the supplier's, the equipment behind them is live and unfused, and breaking a seal is a matter for the supplier, not the householder.