Why do my screws keep stripping?

A stripped screw head is almost always caused before the drill is switched on, by a bit that never fitted properly in the first place.

What you'll need

• Correct bits — Pozidriv, Phillips and Torx
• Drill bits for pilot holes
• A screw extractor or a rubber band, for rescues

Step by step

1. Check whether it is Pozidriv or Phillips.Pozidriv screws have four small extra lines between the main cross. Most UK woodscrews are Pozidriv. A Phillips bit in a Pozidriv screw only touches at the corners and destroys the head — this is the single most common cause.
2. Match the bit size, not just the type.PZ1, PZ2 and PZ3 are different sizes. PZ2 fits most common screws. A bit one size too small rattles in the recess and rounds it off within a couple of turns.
3. Push much harder than feels necessary.Most of the effort should be pushing into the screw, not turning it. Insufficient axial pressure lets the bit ride up out of the recess, which is what cams it out and strips the head.
4. Keep the driver square to the screw.In line with the shank, not at an angle. An angled driver contacts only part of the recess and concentrates all the force on that corner.
5. Use the clutch and slow the speed.Set the torque clutch so it slips before the screw is over-driven, and use a lower speed. High speed generates heat and gives you less time to react.
6. Drill pilot holes in hardwood and near edges.A pilot hole roughly the diameter of the screw's core lets it cut rather than force its way in. It prevents stripping and prevents splitting.
7. Add a clearance hole in the top piece.For joining two pieces, the top one should have a hole the screw passes through freely. Otherwise the screw jacks the pieces apart and the extra resistance strips the head.
8. Replace worn bits.Bits wear out and a rounded bit strips every screw it touches. They are inexpensive — a worn bit is a false economy that costs you screws and time.
9. Lubricate screws into dense material.A little wax or soap on the thread reduces driving torque noticeably in hardwood. Old-fashioned and genuinely effective.
10. Use Torx where you have the choice.The star recess grips far better and effectively does not cam out. For any job with lots of screws, buying Torx-headed screws avoids the problem entirely.
11. Try a rubber band on a rounded head.A wide elastic band or a piece of steel wool laid over the head, then the bit pressed through it. It fills the rounded recess and often gives just enough grip.
12. Use a screw extractor for the worse cases.A cheap set drills a small reverse-threaded hole and backs the screw out. It works on most stripped screws and takes a few minutes.
13. Cut a slot as a last resort.A rotary tool or a hacksaw blade cuts a straight slot across the head, then a flat screwdriver removes it. Only where the surrounding material can take the damage.
14. Drill the head off if nothing else works.Drill through the head until it separates, remove the item, then grip the exposed shank with pliers and wind it out.

Tips

• Pozidriv screws need Pozidriv bits. Most UK screws are Pozidriv and most people use Phillips bits in them.
• Push far harder than you think. Cam-out is a pressure problem before it is a bit problem.
• A rubber band over a rounded head often gives enough grip to back it out.

Common mistakes

• Using a Phillips bit in a Pozidriv screw — The two profiles are different, so the Phillips bit only contacts at a few points. It cams out under load and rounds the recess, usually within the first turn or two.
• Driving screws at full speed with light pressure — Speed generates heat and light pressure lets the bit lift out of the recess. Slow with heavy downward force is what keeps the bit engaged.

If it doesn't work

Questions people ask