How to remove stuck fasteners, part 2: Useful tips

What’s the best way to unstick a stuck fastener? Don’t let it get stuck in the first place. And how do you do that? Let’s look back before we look forward.

Last week, I poked some fun at Zen and the Art of Motorcycle Maintenance author Robert Pirsig for including a chapter in his revered tome that appears to imply you can remove stuck fasteners by merely thinking of a high-quality solution to the problem. I offered a simple solution—don’t let them get stuck to begin with—by using six-sided sockets and penetrating oil. And if that doesn’t work, try heat and wax to wick into and lubricate the threads.

This week I’ll get into the nuts and bolts of removing stuck fasteners. (Pun intended.)

Stripped slotted or Philips screws: Cut a new slot with a Dremel tool

Most of the time, “stuck fasteners” actually means “stuck nuts and bolts.” But every once in a while, you might have a stripped screw head to deal with. As is the case with a nut or bolt, the main technique is to avoid the situation in the first place by using good-quality tools, combined with penetrating oil and heat. But if the slot is munged up, there is a trick you can try.

If you don’t own a Dremel tool (a hand-held rotary cutting tool), buy one. Then buy the “EZ Lock Mandrel” and a pack of EZ Lock thin cutting wheels. These things are a necessary part of the stuckness tool kit. In addition to the cutting wheel’s myriad of uses, you can easily use it to cut a nice new clean slot across the munged-up head of a screw. Do that, soak it in penetrating oil, heat it, and you may be able to get the screw out without needing to resort to more invasive measures.

Rounded bolt corners: Nut-busters and using the next-size-smaller socket

Let’s say that you’ve used your best six-point socket, along with heat and penetrating oil or wax, and you’ve still managed to round the corners off bolt fastener. You have one trick to try before spending two hours drilling the bolt out. Well, maybe two tricks.

(Actually, before spilling the beans, let me repeat that, the longer I do this, the less often I find myself in this situation. Unless the bolt head or nut was already damaged, heat, wax, the right amount of torque, patience, and repeating as necessary usually carries the day.)

You can try those nut-busting extractor socket sets. They’re ratchet sockets of different sizes. Some have metal rods that close in around the rounded edges of the nut or bolt head. Others have curved edges that swirl down diagonally, biting into the fastener as you tighten them. I’ve had mixed luck with both kinds. If you’re going to try one of these, read the reviews and spend the money for a well-reviewed set. Make sure to heat the fastener first, as the odds are you’re only going to get one shot at it before it mangles the head even further.

I’ve had more success with the technique of using the next smaller-sized socket and literally hammering it onto the mangled nut or bolt. You can try stepping down a full size, say from a 13mm to a 12mm (and on exhaust nuts, due to heat and corrosion, sometimes the nut has lost enough metal that it’s already nearly a size smaller), but you can also take advantage of the fact that sizes of metric and English sockets intersperse to some degree.

For example, if you’ve rounded the corners of a 13mm bolt, a half-inch socket is just a bit tighter. If you’ve rounded a 12mm, nut a 7/16-inch socket is quite a bit tighter while being slightly larger than an 11mm. I’ve also had good luck with banging on judiciously-sized Torx sockets. Whatever you have, find a socket that’s one size smaller but will go on with, uh, persuasion, re-apply heat and penetrating oil or wax, hammer the socket on while taking extreme care not to burn yourself on the nut you’ve just gotten red hot, then apply torque. Air tools are great in applications like this where you may have one shot at it. Remember: If this doesn’t work, you’re likely drilling, so make it count.

The dreaded drill

Ok. You’ve already rounded the corners off the bolt, so there’s nothing left to grab onto. Or you’ve snapped the head clean off. If the bolt is holding two exhaust flanges together, you can reach between the flanges with a Sawzall or Dremel tool with cutting wheel and cut the bolt in half. If not, you have few options beyond drilling.

The classic snapped-off bolt head that grinds your entire car day to a screeching halt.
The classic snapped-off bolt head that grinds your entire car day to a screeching halt. Rob Siegel

There is one option, if you have welding equipment. Some folks report that spot-welding a metal bar onto the snapped-off or rounded bolt gives you a lever-arm to turn, along with an additional benefit: The act of welding, the passing of high current through the metal, often helps to break the bond of corrosion. Unfortunately, I don’t weld, so I have no first-hand knowledge of this technique.

If you are preparing to drill, you need three things:

  1. A good center punch. You need to make a clear, well-placed starting hole for the drill. If it’s off, you won’t be drilling on center, and that will create problems.
  2. A good corded drill. Don’t do this with a cordless drill. You’ll be at it for too long. It’ll likely run the battery down. And don’t use a cheap or ancient corded drill that may overheat.
  3. The best set of drill bits you can buy. Read the reviews on Amazon and either order online and wait, or run down to your local hardware store. You can make up your own mind on carbide versus titanium, but don’t cheap out. Spend the money. Believe me, when you’re lying under the car, trying to do this with old dull bits, you’re going to wish that you’d spent the forty bucks for new good ones.

Some folks swear by left-handed (reverse-threaded) bits, and say that the act of drilling with them, the left-twisting—plus the heat and vibration—helps loosen the stuck bolt, and that after one pass with a left-handed bit, the bolt is ready to come out with an EZ-out. I’ve tried left-handed bits and have not found them to have any such magical properties. If you find otherwise, more power to you.

Left-handed drill bits. I was not impressed.
Left-handed drill bits. I was not impressed. Rob Siegel

If there is any way to reduce the amount of metal you need to drill through by cutting the head or the tail off the snapped bolt, do it. Drilling is a slow process. You want to do as little of it as you can. A few years back I snapped a pinch bolt on a strut housing. The fact that the pinch bolt went through a slotted collar allowed me to use a Dremel tool to cut it at the slot and pull the non-threaded (and thus non-seized) half out, lessening the length of bolt I needed to drill through by half.

Cutting a pinch bolt using a Dremel tool.
Cutting a pinch bolt using a Dremel tool. Rob Siegel

Pulling out the non-stuck half.
Pulling out the non-stuck half. Rob Siegel

If there is any way to remove the assembly holding the snapped bolt and put it in a drill press that will allow more precise alignment of the bit with the bolt, do it. Often, there’s not. In fact, the bolt you snapped is usually the very one you’d need to remove in order to get the assembly out of the car.

If you can put the assembly with the snapped bolt on a drill press, by all means do it.
If you can put the assembly with the snapped bolt on a drill press, by all means do it. Rob Siegel

The key to drilling out a bolt is to start with a small bit, drill through, then move up to the next size bit. Don’t, however, start with a bit so small that you can bend it with your hands, as it’ll probably break under the pressure of the drill, and then you’re really buggered.

If you’re decently centered on the bolt, are using high-quality drill bits, and get the first bit through without breaking it, the other bits usually go through faster than you’d think, as they’re just enlarging the existing hole.

Don’t use too much speed. Speed dulls drill bits. And use some kind of oil. 3-in-1 is way better than nothing, but a dedicated cutting oil is the best way to go.

As you’re moving up in bit size, be careful. Bits can grab in the hole being drilled. If a small bit grabs, it’ll probably snap, which sucks but isn’t dangerous. But if a big bit grabs, it can cause the drill to twist around and break your finger or your wrist. If you have a drill with a clutch that’ll spin if it gets bound up, use it. If not, an easy fail-safe is that, if the end of your bit has a squared-off shank for the drill’s chuck to bite into, don’t use it—instead, slide the bit farther into the chuck and use the round section of the bit. That way, if the bit grabs, it can just spin in the chuck instead of causing the drill to rotate dangerously.

Once you have a hole of a certain size drilled through the bolt, you will be tempted to try to take it out with an EZ Out. Do not succumb to temptation! Be strong! That path brings only darkness and pain! Seriously, I told you what I thought of EZ Outs last week—throw them into the garbage. If you snap either a drill bit or an EZ Out off in the hole, you’re basically screwed, as drilling through these with DIY hand tools is nearly impossible.

I will say, however, that sometimes in drilling out a bolt—because the drill usually isn’t exactly centered—you’ll sometimes see the threads exposed on one side of the drilled hole. Every once in a while, when I’ve seen this, I’ve been able to get a small pick between the threads and work the remaining section of the bolt free. Of course, I’ve also snapped the tip off the end of the pick, so don’t go for it with too much gusto.

(Next week: Oxy-acetylene, and when you want to get a fastener nearly to the point where it melts.)


Rob Siegel has been writing the column The Hack Mechanic™ for BMW CCA Roundel Magazine for 30 years. His new book, Ran When Parked: How I Road-Tripped a Decade-Dead BMW 2002tii a Thousand Miles Back Home, and How You Can, Too, is available here on Amazon. In addition, he is the author of Memoirs of a Hack Mechanic and The Hack MechanicGuide to European Automotive Electrical Systems. Both are available from Bentley Publishers and Amazon. Or you can order personally inscribed copies through Rob’s website:

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