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I placed neodymium magnet balls ("buckyballs") in the head of some of the screws on my bike as an anti-theft measure, as I've had components stolen off my bike before. Most of them could easily be removed with a telescoping magnetic pick-up tool, but one of them had some rust and grit in it and wouldn't come out. How can I remove it without cutting or drilling out the screw?

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    What sort/size screws are they? Hex (Allen)? Cross-headed (Philips)? And how big are the balls? I think a photo might make it easier to picture the situation and brainstorm ideas.
    – pateksan
    Commented Jun 12, 2023 at 20:22
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    It was a M5 socket head hex screw with a 4mm diameter magnetic ball.
    – Snowball
    Commented Jun 12, 2023 at 20:34
  • Have you seen the LockPickingLawyer video where he demonstrates that it's sometimes possible to drive a sphere further into an Allen-headed machine screw and then use a standard key to undo it? And where in Earth did you get this "buckyball" crap from?
    – Mark Morgan Lloyd
    Commented Jun 12, 2023 at 21:13
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    @MarkMorganLloyd: "Buckyballs" is a brand name of neodymium magnet toys. Brand names typically pay no attention to accurate nomenclature.
    – Greg Hewgill
    Commented Jun 12, 2023 at 21:46
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    use a stronger neodynium magnet?
    – JoSSte
    Commented Jun 13, 2023 at 13:02

6 Answers 6

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Put on safety glasses and use a spring loaded center punch to chip away at the magnet. Neodymium magnets are brittle, so it will eventually crack. You can dig out the pieces of the magnet with the tip of a knife.

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Depending on the surroundings, heat can be used to de-magnetise an item. Downside, this effect requires 80 degrees C or 175 F to start, and potentially higher.

Heat can also help with corroded parts, but there's a risk of damaging anything in the area and above.

If you go this way, a hot air blower is less damaging than an open flame.

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    What about a soldering iron? That might be able to quite precisely apply the heat to the magnet itself. (Since the question talks about accessories, I'd be worried about transmitted heat from a screw at 80C melting plastic mounts.)
    – DavidW
    Commented Jun 12, 2023 at 19:32
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    @DavidW A soldering iron is a great suggestion. Probably not a good idea with plastic parts, but for metal seatpost clamps, fenders, bottle cages, etc, it would work well.
    – MaplePanda
    Commented Jun 12, 2023 at 19:40
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    Note that this may require temperatures up to 400 degrees Celsius (the typical upper end of the range of Curie temperatures seen with neodymium magnets). If the frame is steel this is probably fine, but I would be wary with aluminum (that’s high enough to significantly weaken most common aluminum alloys, at least temporarily), and I would not even consider it around carbon fiber.
    – Austin Hemmelgarn
    Commented Jun 14, 2023 at 1:31
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Use a strong enough magnet. To my knowledge of magnetism, practically every magnet can be overcome by a stronger magnet.

This can be an expensive, but relatively safe and non-destructive method.

Naturally, bear in mind that very strong magnets involve no end of hazards.

A locksmith might have one, as might other tradesmen working in confined spaces: perhaps car mechanics, general handymen etc.

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  • More to the point, the magnet ball will be more attracted to another strong magnet than to the steel screw (which is only weakly magnetized by the presence of the ball). At least as long as the poles of the magnets are oriented the right way, that is — but the ball magnet, being a ball, presumably can and will rotate to align with any other magnet you bring near it. (If it's stuck and doesn't, try adding some lubricant.)
    – Ilmari Karonen
    Commented Jun 13, 2023 at 20:16
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You mention its a Hex socket with a round ball bearing inside.

I'd consider trying to lever the ball out using one or two picks in opposite corners. There should be a small triangle of space in the 6 corners where you can potentially get the point in and behind the median.

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Along a similar vein. putting your drill bit right in the corner void could be enough to crank-out the bearing ball. The sizing has to be perfect, and this could damage the hex socket too. You also risk breaking the drill bit because it will be quite thin, perhaps a 1 or 1.5mm

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Put on safety glasses and use an electric drill with an appropriate drill bit. If the drill has hammer action available then you probably want to disable it.

If the screw's material is tougher than the ball then you might be able to grind the ball down.

If the screw's material is weaker than the ball then you may be able to drill through it to release the accessory. This may not always be worthwhile, e.g. if the mount is an integral part of the accessory, and/or the screw is not easily replaced (perhaps an obscure thread).

A vacuum cleaner might help manage the dust.

I think this may be better than using a center punch because the process is progressive rather than abrupt and therefore it is easier to control.

My only concern is that in some circumstances you might accidentally launch/eject the ball at high speed in a random direction but a similar risk may exist if using the center punch.

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    It may be challenging to get a hole started with a drill. It ain’t easy to drill into hard, convex spherical surfaces.
    – MaplePanda
    Commented Jun 13, 2023 at 17:20
  • @MaplePanda good point. In practice the tip of the drill bit would probably just slip into the gap between the ball and the corner of the hex slot. I guess what happens next depends on the relative hardness and friction between the screw, ball, drill bit and the rust and grit the OP mentioned. It would probably be a matter of trial and error with different drill bit sizes, as well as angles - parallel with the screw thread may not necessarily be the best.
    – pateksan
    Commented Jun 13, 2023 at 19:17
  • My guess is broken drill bit and some swear words.
    – vidarlo
    Commented Jun 15, 2023 at 12:56
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If you have a pressure washer with a zero degree tip, don all the usual safety equipment and use the pressure washer like a Water Pik on the socket. You'll never find the ball after it flies out, but that will prevent you from having to do the same trick twice!

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    Are you sure that water pressure will be enough to dislodge the magnet? The water may not be able to get sufficiently around the magnet to dislodge it against the magnetic attraction or the pressure from the water against the magnet may be more than the back pressure.
    – DavidW
    Commented Jun 13, 2023 at 13:41
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    @DavidW Yep, a zero degree tip will dig the pebbles right out of a concrete surface. Magnetic attraction is no match for that. The tiny corners of the hex socket where the ball isn't will be sufficient to get water behind the ball and force it out.
    – MTA
    Commented Jun 13, 2023 at 14:03
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    Is there any risk of the ball being ejected at high speed and posing a safety hazard with this technique?
    – MaplePanda
    Commented Jun 13, 2023 at 17:21
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    @MaplePanda Yes, of course! That's why you don all the usual safety equipment. Any sensible person who owns a pressure washer already has safety equipment.
    – MTA
    Commented Jun 13, 2023 at 17:43
  • This sounds like the bread trick for removing bearings in a blind hole, but faster. Great idea and welcome to the site !
    – Criggie ♦
    Commented Jun 13, 2023 at 22:58

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