"Stripped bolt" is one name for four different failures: a rounded head, a chewed-out drive recess, stripped threads in the hole, and a bolt snapped off flush. The fix for one wastes your afternoon on another. Here's how to tell which one you have, then the ladder working mechanics follow, in the order they follow it.
The ladder on this page is research: the order comes from the cited mechanic threads and repair guides, not from my bench. The pool pump is mine.
My pool pump. I have on many occasions fought with a stripped bolt. Most recently on my pool pump. I tried WD-40 and larger and larger screwdrivers, and ultimately had to break it and strip it out. I put in a new screw with a bunch of that white plumber's tape.
Extractors. I have not used a bolt extractor.
For the record, my pool pump was a grip problem, and I treated it with oil and bigger screwdrivers. The table below has a column for that approach. It is not the column with the fixes in it.
| What you're looking at | What it's properly called | What fixes it | What will waste your time |
|---|---|---|---|
| Hex corners rounded off; the socket spins | Rounded / cammed head | Undersized six-point socket driven on; locking pliers; a dedicated bolt-extractor socket | Drilling. There's still a head to grab — don't destroy it |
| Phillips, Torx or hex recess chewed out; the bit spins | Stripped drive recess | Screw-extractor bit, a fresh bit hammered in, or grinding a slot for a flat blade | More downward force with the same worn bit — that's what caused it |
| Bolt spins forever and never tightens or comes out | Stripped threads (in the hole or on the bolt) | Thread-repair insert — Heli-Coil or Time-Sert; or replace the bolt if the bolt's threads went | Every extraction technique on this page. Nothing is stuck |
| No head left — a flat or jagged face flush with the casting | Snapped / broken-off bolt | Heat and penetrant, left-hand drill bit, welding a nut on; extractor as a late resort | Leading with a spiral easy-out. See below |
Terms follow the E46Fanatics fastener reference thread and NAPA's stripped-thread repair guide for the thread-insert side.
Two details decide whether this works. Use a six-point socket, never twelve. A twelve-point grips the corners. You no longer have corners. And hammer it on; hand pressure isn't enough to make the socket cut in. If the socket won't start, a step down further usually will.
If there's a shoulder of head standing proud of the surface, locking pliers clamped hard and turned slowly are the other free option, and they beat a socket on a bolt that's rounded unevenly. Neither costs you anything, and both leave every later option still on the table. That is exactly why they go first.
The practical move is to soak before you start escalating, not after you've already chewed the head further. Which product is worth buying is its own argument: six independent tests disagree with each other, and the most-recommended can on the forums finished last on camera. I scored that whole fight in the penetrating oil guide.
This isn't a fringe opinion. In a 2020 Garage Journal thread on extractor sets, one poster put it bluntly. "Do not use any Round long spiral Ezouts unless you want to practice removing broken ezouts." The same thread's preference runs toward straight-fluted and splined extractors instead of tapered spirals. Lisle, Irwin's multi-spline sets, Proto and Snap-on come up by name. A straight flute loads the broken bolt in shear instead of trying to split it open.
The counterweight: extractors do work, on the specific case they're built for, a bolt that snapped because it was over-torqued, not because it was rusted solid. If the fastener let go without a fight, an extractor has a real chance. If it snapped while you were leaning on a breaker bar against thirty years of corrosion, the corrosion is still there. The extractor is walking into the same wall that broke the bolt.
Heat and cool the surrounding casting repeatedly. Expansion and contraction is what breaks the rust bond; several mechanics in the Garage Journal thread describe cycling a torch on and off rather than just cooking it. This is also the quiet reason the welding trick works so well. See step 3.
Drill with a reverse-rotation bit. If it bites, the cutting direction is also the loosening direction and the bolt backs itself out. If it doesn't, you've lost nothing: you now have the centered pilot hole every remaining method needs anyway. One mechanic put it exactly right: "Sometimes they break things free. If they don't, you have the hole you needed anyways." One UK how-to guide puts the spin-out rate at roughly one bolt in five. That is one source's field figure, not a measurement.
The prerequisite nobody skips: "The key is drilling a hole, square and centered." Center-punch it. An off-center hole eats the threads on one side and takes thread repair from optional to mandatory.
If you own or can borrow a welder, this is what the professionals reach for. Lay a washer over the stub, drop a nut on it, and weld through the middle to the broken bolt. The weld is not really the point, and one poster in that thread said so plainly. "The weld itself often isn't that strong but by welding the bolt you heat it." You're getting localized heat right where the rust is, a brand-new full-size head, and a bolt shrinking as it cools. That's three problems solved at once, which is why it beats an extractor set on a seized fastener.
Now an extractor is reasonable: the hole is centered and the joint has been heated. Failing that, step the drill up progressively until you're just under the bolt's diameter, then chase what's left of the threads with a tap. If the threads don't survive, a thread insert restores the hole to full strength.
The only tool here whose failure mode is still useful: a bit that doesn't back the bolt out has still drilled the centered pilot hole every other method needs. It does half the job by failing. Cobalt (M42) if you have the choice.
Not a purchase for most people. The sockets are already in your drawer; the new part is hitting them with a hammer. Six-point, one size down. Twelve-point sockets grip the corners you already destroyed.
Heli-Coil or Time-Sert, sized to the fastener. Nothing else on this page helps stripped threads; this is the fix, and an off-center drilling job usually ends here anyway.
No brand picks and no buy buttons in this section, on purpose. Which specific set is worth owning is a separate question. Project Farm has run extractor sets head-to-head, and the video is in the sources below. I have never used a bolt extractor. Given the easy-out section, I am counting that as a win.
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