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Are there compression plugs specifically designed for metal steerer tubes, that is:

  • their expanded diameters take into account the thinner wall of the metal steerer tubes relative to that of a carbon steerer, so the plug doesn't need to be shimmed

  • their expanding section's height (and thus the plug's overall weight) is reduced relative to the carbon steerer version because there's much less risk of rupturing a metal steerer by outward force of the expander being concentrated in a small section of the inner wall

If you've got a metal fork you're likely to be less concerned about grams than someone who opted for a carbon fork. Ease of installation and the need for one less tool are compelling reasons for such a device, so I'm hoping somebody makes them.

I ask the question in the context of the many threads on various bike forums about installing star-fangled nuts and the risk of installing the plug so it sits crooked inside the steerer tube; also the tools used to install these star-fangled nuts properly (compared to using a broom handle, say) are fairly expensive, with the less-expensive tools receiving a fair number of negative comments from buyers.

P.S. Something like this, if it were made of steel, not aluminum, would do nicely for a cromoly fork (it comes in two sizes, the larger up to 27mm I.D.)

ExtraLite UltraStar

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    Isn’t a star nut lighter and cheaper?
    – Michael
    Mar 19, 2022 at 17:32
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    The top-tier tool to install a star-nut costs over $50 shipped, less expensive ones about $25. So a star-nut is actually more expensive than a device that wouldn't require a special tool in order to be installed properly. A star-nut weighs almost nothing but an expander wouldn't add all that much weight, especially when the fork itself is made of metal. The main thing is that the plug would have to be made for metal tubes so it grips securely.
    – Tim
    Mar 19, 2022 at 18:39
  • I installed a small star nut using an old bolt with the same thread. Simply lined it up and tapped it in with a hammer. The right tool would be nice but overpriced for a once-off.
    – Criggie
    Mar 19, 2022 at 20:34
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    @Criggie I'm refining a 3D printed star nut tool that can be easily and cheaply made. Just having some issues with long-term cracking at the moment.
    – MaplePanda
    Mar 19, 2022 at 21:33
  • @MaplePanda Nice! I wonder if there's a fresh question here "what bike tools can I print ?" and perhaps the same for parts/accessories.
    – Criggie
    Mar 19, 2022 at 21:38

1 Answer 1

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I have an old Reynolds Ouzo one on a Fox aluminum steerer in my living room right now. Most plugs have a fairly wide range they can expand into and can do both aluminum and carbon, although it is true that you can come up with exceptions.

The distinction at play in terms of what will work is really more steel versus everything else than it is metal versus carbon. Steel steerers are much thinner wall, especially fancy ones. Star nuts themselves sometimes wind up not being able to bite into steel steerers even if they're nominally for the correct diameter fork. (Not a common problem, but I've seen it). If you want to make a plug work in a steel steerer, it's basically always going to be luck of the draw. Plug manufacturers generally don't offer a max expansion/min wall thickness type spec.

Putting a carbon plug in a metal steerer is something that could make sense in a pinch if you don't have the tool, i.e. putting together a bike for yourself and you don't want to bother buying or making a tool. That said, it's all technique, and the problems people have with installing star nuts basically all boil down to expecting a tool to substitute for good technique and practice. Most of the tools these days are the guided type where one element is a tube that slips loosely over the steerer. The big trick with this style is let the outer tube float loosely as you make your strikes. You have one hand on the hammer and the other cradling the fork under the crown, and the fork is only supported there (never ever under any circumstances with the dropouts on a hard surface, ever). That's how you make it self-align. Problems with going in crooked tend to happen when you hold the tool/guide to try to help the alignment, which winds up resulting in misalignment at the moment of impact. Use moderate force strikes only, no more than is needed to get the nut's tines to conform. Go slow and if it starts getting crooked, leave the nut in, unscrew the tool from it, take the guide off, do very light strikes to straighten it, and then put the guide back on. Star nuts want to go in straight, you mostly just have to facilitate it with technique that doesn't introduce a misalignment.

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    I have one of the $25-tier tools on order. But I'd much prefer to not have it depend on my technique :-) Thanks for the tips. I will bear them in mind.
    – Tim
    Mar 19, 2022 at 18:43

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