This is the opposite to a common DIY question, where people have a stripped or rusted screw or bolt and want to unscrew it.

In my case, I've just built a bike shed. It's held together by thin bolts that have a cross-cut head, (see image below), where the head is on the outside of the shed. I want to disable these so that it's not possible for someone to unscrew them to get into the bike shed. (I'm a bit paranoid because my last bike was locked to the front wall of the house, near the shed, and was stolen)

A bolt with a cross-cut head

Ideas I've had so far are:

  • Using a mains-powered drill and a large HSS drill bit, drill into all of the heads to effectively strip off all, or most, of the cross cut.

  • Covering each head in some kind of substance which will dry rock-solid, and not fall out of the cross-cut, even after years of weather, and which can't simply be sliced away with a sharp blade.

Any thoughts or suggestions? Eg, a suitable substance for option b? I'm trying to do this project very cheaply (it's all reclaimed wood for example) so it would need to be something I can get a tube of without spending loads of money.

PS: Please don't suggest that I should have used non-unscrewable security bolts in the first place :)

Also, I would still like to be able to take it apart from the inside, by undoing the nuts from the bolts, so solutions which permanently cripple the entire bolt (eg by bending it) are not ideal.

  • I trust you've also thought about the hinges (screwed on the inside, can't just knock the pins off), the padlock/hasp (padlocks are pretty awful but I've never seen a theft where one was picked/shimmed, mostly they're just cut), the possibility of just picking the shed up (is it bolted down? Or can three guys just lift if off?), and a proper anchor inside for the bike lock... (if you're going to be paranoid--and I've lost enough bikes to be paranoid too---you might as well go all the way). There's active security (camera/bluetooth alarm/etc) but maybe that's going too far....
    – 2e0byo
    Commented Mar 8, 2023 at 20:51
  • Would red loctite work?
    – DKNguyen
    Commented Mar 8, 2023 at 23:09
  • 1
    put solder in the screw cut. if you decide to take it apart in the future you can remove it with a soldering iron.
    – JoSSte
    Commented Mar 9, 2023 at 7:00
  • 1
    @DKNguyen. I missed a word... was supposed to say "what dknguyen SAID" I.E. agreeing with you!
    – Kyle B
    Commented Mar 10, 2023 at 14:47
  • 1
    @KyleB Understood
    – DKNguyen
    Commented Mar 10, 2023 at 14:58

9 Answers 9


You could add another locking nut on the bolt inside the shed -

Two nuts on a bolt, the narrower nut first

You wont be damaging the rust protection of the bolt and it is an easy addition if the bolts are long enough.

Here's some useful information about the use of lock nuts. The narrower nut should go one first and the nuts should be tightened against each other. Also use a washer to prevent the bottom nut from gripping the wood.

  • 1
    Or replace them with nylocks.
    – Huesmann
    Commented Mar 8, 2023 at 20:47

You can grind the head smooth but the problem is you then weaken the bolt. A better solution is to buy some smooth headed carriage bolts similar to the one shown below from Lowes. They come in various sizes and also come in stainless steel.

enter image description here

  • Don't carriage bolts generally rely on the square "neck" to register into a corresponding dedent/cutout in the material to hold them fixed against the back-torque of the driven nut? If the bolts being replaced had a fully round shank and had the bottom of the head sitting flush to the material (as one would expect for the side being driven), then you can't really just substitute a carriage bolt.
    – R.M.
    Commented Mar 9, 2023 at 0:38
  • 2
    @R.M. The OP's using wood for the shed so the square wouldn't be a problem that a wack with a hammer wouldn't solve, Plus, not all carriage bolts have a square.
    – JACK
    Commented Mar 9, 2023 at 0:50
  • The square is usually wider than the rest of the shank, @R.M., so unless the hole is wider than the bolt needs, it should work. And with a wider hole, OP could use bigger bolts.
    – SQB
    Commented Mar 9, 2023 at 7:11

Just use a grinder to grind them smooth. The dedicated bike thief will use their grinder (which they carry for cutting bike locks, padlocks, etc.) to grind them all the way off, of course. Except they won't bother, as they'll just cut (or freeze with liquid nitrogen and shatter) your padlock and kryptonite lock to get the bike, rather than taking the shed apart.

If you have that sort of bike thief pressure, you just need to put the bike in the house, or have an active alarm system on the shed, at least. Using a padlock rather than a normal sort of guarded deadbolt on the shed door plays in favor of the bike thieves' normal methods and equipment.

A better choice would have been to use carriage bolts, which are entirely smooth on the "show" face, but actually have a square section to keep them from rotating in the hole so you can remove them from the other side when you want to. Since you comment that you would like to be able to disassemble from inside, you should replace them with carriage bolts.

  • Problem with grinding it smooth is he's hosed if he ever wants to REMOVE them again. Weakens the heads quite a bit, too.
    – NerdyDeeds
    Commented Mar 9, 2023 at 0:02
  • 1
    Can cut a new slot or grind them completely off at that point. There really isn't much added strength in the part of the head that's already cut into slices to make slots. The strength, such as it is, is below that level. Also, see last paragraph.
    – Ecnerwal
    Commented Mar 9, 2023 at 0:08
  • I would make the counterargument that such a tactic depends largely on the flavor of the bolt. In a hex-headed bolt that has been rounded, say by using the wrong size socket to drive it, I'd totally agree with you. But OP mentioned explicitly a drive system, and the included photo suggests they're round-headed bolts. Their drive system (per ISO 2380-1:2004) extends down into 75% of the head's thickness. "Grinding it smooth," therefore would reduce its effective strength to below that of the shoulder. A punch and a mallet could knock it out. And there'd be virtually nothing left to slot INTO.
    – NerdyDeeds
    Commented Mar 9, 2023 at 0:47

Frame challenge: You're overthinking this. The shed itself is sufficient as both deterrent and obfuscation.

You don't need to worry about someone disassembling the shed by undoing enough screws to pull the bike out, for the same reason you don't need to worry about someone ignoring the screws and just cutting a hole in the wall: it will take too long, and the thief doesn't know ahead of time whether it will be worth the risk and effort.

When your bike was stolen, it was easily visible, and the thief spend 5 seconds breaking/cutting the lock.

  • 2
    Sadly although I agree that removing the bolts is unlikely, where I live this is not overthinking it, and putting a bike in a shed only means they'll take it at night rather than in the day.
    – 2e0byo
    Commented Mar 8, 2023 at 20:48
  • 5
    @2e0byo You're still ignoring the sheer difference in complexity of attack vs normal breaking and entering. Removing enough bolts quickly will require power tools. Bypassing (most) consumer locks takes a couple very small tools and usually mere seconds. Removing non-security hinges is the same. Or just hammering the latch off. Without OP showing how secure the normal entrance is the discussion about wall security is over the top.
    – Logarr
    Commented Mar 8, 2023 at 21:05
  • 3
    @Logarr oh I commented that above, I just mean that this level of thinking is not overthinking it, at least round here, but I agree that any attack which requires removing > 2 bolts is very unlikely, let alone taking out a sizeable portion of a wall. But it's not necessarily true, sadly, that the shed is sufficient deterrent or obfuscation.
    – 2e0byo
    Commented Mar 8, 2023 at 21:08
  • 2
    I'm actually of the opinion that y'all are overthinking his QUESTION. He didn't ask, "do you guys think I need to stress this?" He asked how he could prevent the need. Fact is: one CAN work a bolt free with just a driver. Moreover, since it can be done with just a HANDHELD screwdriver, it's a virtually SILENT approach to penetration. Finally, while I have no clue where OP lives, I HAVE lived in places with crime at the levels he fears. I walked out of the shower once to find that, in the 15 minutes I'd been in there, someone had unbolted my ground-floor WINDOW to steal my laptop off my desk.
    – NerdyDeeds
    Commented Mar 9, 2023 at 0:01
  • Even though this doesn't answer the question (and so doesn't get the tick) I think you're right. Security generally is not about making things impossible, it's about making them time consuming. My neighbourhood's generally pretty safe - it's a boring quiet residential neighbourhood and the house is a mid terrace with steps up to the front door (the bike shed is next to the front door) and the thief would be quite visible. When it was stolen before the bike lock was a cable type and they just sawed through it. Commented Mar 9, 2023 at 11:05

You can drill a hole through the shaft of the bolt below where the nut will be and then run something like a cotter pin through it, which will stop the nut from being able to come off. But this approach will only be practical with the right tools and some time investment. You also might have to plan some effort in cleaning up the threads after drilling into them.

  • I'd have thought that drilling through the bolt would mess up the thread so much that it would be impossible to remove the nut anyway, cotter pin or not. Commented Mar 9, 2023 at 11:08
  • 1
    @MaxWilliams Not at all! The trick is to fully thread on the nut prior to drilling the hole. Yes, the bit can partially chew up a couple threads, especially if the operator isn't firmly set when starting the hole and there's chatter (when the bit skitters on the surface, though this can be prevented by whacking a nail or another screw with a hammer to provide an indent to start with). But, once the hole is drilled, simply unscrew and rescrew the nut several times. The inside threading on the nut has nowhere to go, so will force the bolt's thread back into alignment, effectively resetting them.
    – NerdyDeeds
    Commented Mar 9, 2023 at 12:18

If you're expecting that any disassembly will occur from the inside, would it be possible to tack weld the bolt head to the exterior of the shed? Of course this will damage any paint or coating, and would require compatible metals.


I used to work in a bank. The security officer told me that it is impossible to create totally burglar proof valves. What you can do is to delay the entry enough to be able to take action.

Same goes for a shed with a bike inside. What you can do is to make it enough time consuming or noisy for the thief to either abstain from trying or giving up.

There is very little use in locking down the nuts if you simply can walk right through the planks of the shed. So what you could do are things that make it slower for the thief and add "noise" or alarms.


  • noisy alarm inside the shed
  • cameras with lights
  • make the most obvious bolts and nuts into "blind" nuts, ie double nut on the inside and turning the nut simply turns it.
  • add a metal "cage" inside the planks of the shed
  • You've now got me thinking about some sort of mechanism I could add which always makes a loud noise (mechanically, somehow, not relying on any electronics or anything) when the roof is opened (i take the bike out vertically through the roof since the shed is partially below ground level) Commented Mar 10, 2023 at 11:57

You can probably buy replacement screws with the same thread and length but a security head. Security Torx needs a special Torx driver. Tri-wing is just plain unusual, as is snake-eye.

And then there are the screws designed to be impossible to un-do. One sort has a hex head attached to a domed head by a thin neck. When you screw it up tight the hex head shears off heaving nothing to apply a driver to. Another sort has a head that allows a flat bladed screwdriver to apply full torque clockwise, but the same driver will cam out anti-clockwise.

Finally, you can use ordinary Philips, Pozi or Torx head screws and fill the receptacles with epoxy glue once everything is assembled. Torx will probably be the hardest to scrape epoxy glue out of. Even with the ones you have, epoxy glue will slow a thief down a lot and cause him to make noise. (And at the same time if you do want to dismantle the shed, it'll be easy to remove the epoxy with a Dremmel disc).

It all depends on whether you might want to dismantle the shed at a later date, and if so how much work you want that to be.


Let them steal it. Contact an insurance agent about an appropriate policy to cover the anticipated loss. In the long run it would seem to be cheaper to insure the bike than to spend time and money trying to make it "unstealable".

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