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Removing Broken Screws & Bolts

A seized screw, a rounded-off head or a bolt snapped off in the hole - work through these steps in order, starting with the gentlest. Most broken screws come out at step 1 or 2; the later steps are for the stubborn ones.

1. Free the thread first

Whatever is left of the screw, it came out hard because the thread is locked by rust, thread-locker or galling. Free that first and everything after is easier.

• Penetrating oil - soak it, leave it as long as you can (overnight is best), and soak it again.
• Shock it - a few sharp blows with a hammer on the screw or a punch cracks the rust in the thread and lets the oil in.
• Heat - heat the metal around the screw so it expands away from it. Heat also breaks down thread-locking compound. Let it cool a little and work it backwards and forwards.
• Work it, don't force it - a quarter turn out, a little back in, then out again. Forcing a seized screw is how it snaps.

2. If there is something to grip

• Grip (locking) pliers clamp onto a rounded head or a stud end and lock there, so all your effort goes into turning.
• File two flats on a round head or stud and use a spanner.
• Cut a slot across the head with a hacksaw and use a flat screwdriver.
• Weld a nut on the end of a snapped stud - the heat from welding helps free the thread as well.

For a snapped stud with some thread still showing, a stud extractor grips the plain end and turns it out with a spanner or ratchet.

Grip pliersSYKES stud extractor

3. If the head is stripped or rounded

A hand impact driver is the tool for this. Fit the right bit, hold it square, and hit the end with a hammer: the blow drives the bit hard into the head at the same moment as it turns, so it shocks the thread loose without cam-out. Set it to undo before you hit it.

Use a bit that fills the recess properly - a worn or undersized bit is how the head got stripped in the first place.

Hand impact driver

4. If it has snapped off flush or below the surface

Make a flat and a start for the drill

A snapped screw rarely breaks off flat. Never start a drill on a sloping or jagged end - it runs downhill, off centre, and into the thread on the low side, ruining the hole.

Best: use the DORMER P100 and P101 carbide burrs together in a die grinder - the P100 end-cut burr grinds the broken end flat and the P101 cuts a start for the drill, dead centre, without touching the sides of the hole. With these you do not need to centre punch.

Otherwise: file the end as flat as you can and centre punch it exactly in the middle.

Either way, everything after this depends on the hole being central. Start with a small drill and work up.

DORMER P100 burrsDORMER P101 burrsCentre punches

Try a left-hand drill

A left-hand drill (DORMER A101) cuts turning anticlockwise - run your drill in reverse. As it drills it tries to unscrew the broken piece, and very often it grabs and winds it straight out. If not, you have the right hole for an extractor anyway.

DORMER left-hand drills

Screw extractor

Drill to the size marked for the extractor, tap it in, and turn it anticlockwise with a tap wrench - slowly and evenly, with both hands.

• Tapered extractors bite harder the further they go in and the harder you turn. The taper wedges outwards, though, and can expand the broken screw tighter into its thread.
• Parallel (straight-flute) extractors are tapped in and grip along their length without wedging - the better choice for a screw that is properly seized.

We stock SYKES extractors in both types.

Tapered extractor sizes and drill sizes

Tapered extractors are numbered 1 to 9 (most sets are 1-5 or 1-6).The harder the bolt, the wider you can drill: a high-tensile bolt is less likely to expand into its thread as you force the extractor in, so it takes a bigger hole and gives the extractor more to grip. A soft or mild-steel screw, brass or stainless spreads easily - use the smaller drill. Never drill so wide that you reach the thread.

DORMER M900 series figures. High tensile means 75 tons/sq in and over - roughly grade 10.9 and 12.9 bolts and socket cap screws. Other makes number their extractors the same way but the drill sizes can differ a little; if your extractor or its packet gives a drill size, use that.

SYKES parallel extractor setSYKES tapered extractor

5. Last resorts

• Drill it out. Drill up through the centre to just under the tapping size of the thread, then pick the thin shell of thread out with a pick or a scriber, and run the right tap through to clean it up. The tap drill chart gives the size.
• Re-tap oversize. If the thread is damaged, drill and tap to the next size up and use a bigger screw.
• Thread insert. Where the screw size must stay the same, drill out and fit a thread repair insert.
• Broken extractor or tap in the hole? These are hardened right through, and drills and burrs make little impression - trying usually just damages the hole and its thread. In practice the only reliable way out is spark erosion (EDM) at a machine shop, which burns the broken piece out without touching the part.

Taps

Stop it happening next time

• Use anti-seize on threads that see heat, water or stainless steel.
• Tighten to the right torque - see the bolt torque chart.
• Use the right size bit or spanner, square to the fastener, and replace worn bits.
• On stainless, go slowly - stainless screws in stainless threads gall and lock solid if run in fast or dry.