What to Do With a Stripped Screw

Stop turning. Every additional attempt with the bit that failed removes more of the recess, and the recovery methods that need a partly intact recess are the cheap ones.

Work out why it stripped, because that decides what will work now. A recess that is polished smooth in the middle but sharp at the mouth was driven with an undersized bit. A recess with all four corners opened out was driven with the wrong family, usually a Phillips in a JIS or Pozidriv. A head with a bright ring around the recess mouth had a bit that was seated at an angle.

Then check whether the screw is even meant to come out under normal torque. Threadlocker, corrosion and paint each add resistance that no recovery method removes, and fighting them through a damaged recess is how a soft problem becomes a drilling job.

A correct, unworn bit pressed hard and turned slowly is the first thing to try, and it works more often than people expect. Downward force is what keeps a tapered bit from climbing, so put your weight over the driver rather than pulling on the handle.

A wide rubber band or a piece of steel wool laid over the recess fills the worn clearance and gives the bit something to bite. It costs nothing, it takes a minute, and it fails immediately if the recess is too shallow to hold the material.

Friction compound, sold for this purpose or borrowed from a tube of valve-grinding paste, works on the same principle with grit instead of rubber. It leaves abrasive in the assembly, so it belongs on a bracket and not inside a gearbox.

All three of these need the recess walls to still exist. Once the walls are gone, no amount of grip material replaces them.

An extractor is a left-hand tapered spiral. You drill a pilot hole into the head, drive the extractor in counterclockwise, and its taper wedges tighter as it turns until it backs the screw out.

The pilot hole size matters more than the technique. Too small and the extractor will not bite; too large and you have removed the material the extractor needs to wedge against. Follow the size printed on the extractor rather than guessing.

Extractors are hardened well above the hardness of ordinary drill bits. That is what lets them bite, and it is also the whole risk: a snapped extractor left in the pilot hole cannot be drilled out with anything in a normal garage. Once that happens the options narrow to specialist tooling.

If the head stands proud of the surface and there is meat in it, a thin abrasive disc in a rotary tool will cut a straight slot across it. You then drive it with a flat blade that fills the slot you just made.

Cut deeper than feels necessary. A shallow slot rounds out under the same load that ruined the original recess, and you only get one attempt at cutting into a head that is now thinner than it was.

This method removes head material, so it competes with drilling rather than preceding it. If the head is countersunk flush, there is nothing to cut into and you should skip to drilling.

The last method accepts that the screw will not turn and separates the head from the shank. Drill straight down the axis with a bit sized close to the shank diameter. When the head releases, the part comes away and you are left with a stub standing in the threaded hole.

That stub is usually easy. With the clamping load gone, the shank often turns out with pliers or with a light touch from a chisel. If it does not, you are into drilling and retapping, and the hole is very likely to end up a size larger than it started.

Drilling into a casting removes thread as well as fastener. Decide before you start whether a helicoil, a thread insert or a larger fastener is acceptable in that hole, because you will not get to make that decision afterward.

Identify the drive family before the size. A Phillips bit in a JIS screw strips at a torque the screw was never near, and no amount of care with sizing helps if the family is wrong.

Replace bits when they lose their edge. A bit is a consumable, and a worn PH2 costs less than the hour a drilled-out screw takes. Bits that have driven impact fasteners are done for precision work whatever they look like.

Seat the driver square and push before you turn. Most stripping happens in the first quarter turn, when the fastener is at its tightest and the driver is least settled.