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I've been searching on Google for the last hour trying to figure out if this is some kind of security nut. It's on a Shimano hub on the rear wheel.

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    Can you tell us any more about the bike, and why you're removing the wheel and IGH from the bike ? It is yours, or you're allowed to work on it, right? You're not swiping parts from a rental bike in its stand ? – Criggie Nov 23 '19 at 23:08
  • @Criggie the picture looks like it's indoors, so unless they've swiped the entire bike it's probably legit – Chris H Nov 24 '19 at 7:56
  • This looks surprisingly similar to my 12x142 Shimano E-thru axle nut, except that it was designed by me without any prior knowledge. The nut usually looks like this. – Klaster_1 Nov 24 '19 at 9:45
  • If you have access to a lathe and drill I would drill four holes in a piece of metal at the right pitch for the slots. Drill and bore the middle out and drill a cross hole for a tommy bar. Insert four dowels into the four holes. Put the tommy bar into the cross hole and unscrew it. – Bonzo Nov 24 '19 at 17:59

A security nut is exactly what it is. I've seen similar ones on public bike share bikes. As to where you get the tool for it, no idea. Other ones I've seen have been shrouded; this looks like you could get a pipe wrench on it to replace it with a normal one.


Its a rear wheel security axle nut, with an anti-rotation washer underneath. I see a band brake or a roller brake, and a Shimano Nexus (8?) internally geared hub, which are reasonably valuable, hence the security nut.

If you want to get it off with a minimum of damage, I'd make a tool.

  1. Get an old set of bootpinch pliers and round off the cutting faces with a grinder so they match the profile of two opposite indents. Then unwind it like a wrench.

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  1. You could make some sort of a socket to go over the nut - but this would be difficult, and I'm not sure how one might make the lobes.

For a once-off I'd use a Pipe Wrench or some Sliding Jaw Pliers and marr up the surface, with the intention of replacing it with a normal nut.

Also, if you have some round wire that is the same diameter as the indents, cut four short lengths and tape them into the indents. This will take the load/pressure of your tool off the outside surface of the nut.

Some people might attempt to wrap the nut in cloth or leather or something to protect the surface from the tool, but personally I find that rarely works for me.

You could possibly grind some flats into the nut, but that will weaken it, you risk damaging the frame, and won't be a great long term solution compared to just replacing the nut.

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    I recently managed to get a similar nut (worse, it was slightly tapered) off a scrapped ex-rental bike using mole grips (vice grips). When I build the new wheel I'll fit it with normal nuts. Another destructive option is grinding a pair of flats on the nut, to use a normal spanner. – Chris H Nov 24 '19 at 7:54
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    "wrap the nut in cloth or leather or something to protect the surface from the tool" -- I've done this with mixed success. It really depends on things like how tight the fastener is, and how durable it is. Fasteners made from metal that's too soft get squished and if they are too tight, you won't get enough friction between the protective layer and the fastener to move it. You also need to watch out for the pliers cutting through the material. But, fasteners with some variation in their surface (including the notches on the nut here) often allow pliers to grip well through chamois or similar – Peter Duniho Nov 25 '19 at 1:58
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    Another way is wrapping copper wire around the nut and then use pliers. Copper won't damage the nut. – Arne Nov 25 '19 at 8:48

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