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I have an oldschool SunTour 6-speed freewheel, where the smallest sprocket screws on the freewheel body to lock the larger sprockets in place.

Cogset on the freewheel body with the smallest locking sprocket loose

It's a normal right hand thread, so as you pedal in the highest gear, you are constantly tightening the locking sprocket. This means these can get ridiculously tight, as had happened with this unit. What would you recommend for the threads to keep the locking sprocket from seizing? Grease, anti-seize i.e copper paste, threadlock or something else?

My thoughts on the different compounds:

  1. Grease

We don't want any lubrication here, we just want to make sure that there is something between the freehub body and the sprocket to keep the weather out and keep them from permanently binding. Doesn't sound like a typical place for grease.

  1. Anti-seize

While it seemed like an obvious choice, I wasn't sure if there were some issues with using an anti-seize compound in this kind of scenario. Also, there are various different anti-seize compounds out there, and I haven't done too much research about the differences between the various types.

  1. Threadlock

Since the sprocket might experience significant torque during heavy pedaling, it could break a soft threadlock. I could use a stronger threadlock than the soft blue one I have, but then again, could it make the sprocket difficult to get loose in the future? A thread that experiences a changing torque doesn't sound like a typical place for threadlocker anyways.

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One of the things anti-seize exists to do is provide the best possible protection against stuck or damaged threads in applications like this where the parts are tightened repeatedly under working loads. It will tend to be the most effective and require the least breaking torque. Where anti-seize becomes more necessary is titanium or stainless-in-stainless interfaces, but that doesn't mean it's not a good choice elsewhere. Threaded cogs (especially track cogs) can be difficult to undo in some instances, usually when a very powerful rider is involved and/or when the tools used are limited in strength (chain whips), so by using anti-seize you've at least done what you can to make it as easy as possible.

Anti-seize has solids in it so you want to keep it out of bearings. You don't have to be too fearful of this on a bike application near a bearing system; just don't overdo it, and wipe away any excess.

As for which anti-seize to choose, the ones I use are always just copper "all bicycle application" ones so I don't have great advice there. I've always found it to be a rabbit hole of a topic. I think some others marketed for bikes are also silver- and/or nickel-based, but my rough understanding is that for the kinds of conditions and temperatures bikes encounter, it doesn't matter.

Grease (speaking here of NLGI #2 bearing grease of the sort most often used on all kinds of bike applications) is not super far behind for most thread applications and is fine to use if it's what you have (again ti and stainless-in-stainless being the major exceptions).

Don't use threadlocker in this spot or ones like it. The interface on freewheel and track cog threads needs more lubrication and resistance to corrosion than it's good at providing, and loosening isn't an issue by nature. Threadlocker provides acceptable corrosion resistance in the applications it's good for because it sets up and forms a seal, but I don't think that would work reliably here (I'm speculating a bit here but I also think there's no reason to chance it).

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The odd-one out here is threadlocker - it will make the removal process even harder. You do not have a problem with the thread self-undoing. I would strongly suggest not using threadlocker product here.

Grease is fine, copper-paste is excellent. Use the one you have. Both are fairly resistant to being washed out.

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  • I think the idea with (strong) threadlocker is that it would prevent further tightening. I’d only try it if it’s possible to heat up the part easily.
    – Michael
    Oct 27 at 5:41
  • @Michael "strong" thread locker needs a gas torch to soften it. One's freewheel hub would cook, the bearing balls would get upset, and the grease would burn out of it. Please don't use thread lock of any brand or strength. The copper paste would be best, with grease a reasonable second place IMO.
    – Criggie
    Oct 27 at 6:14
  • Yes, I don’t think it’s the optimal solution, but it could work. Red Loctite is removable after being heated to 260°C which should be achievable with a hot air gun (after bearings, grease and any rubber sealing rings have been removed).
    – Michael
    Oct 27 at 8:05
  • 1
    @Michael Doesn’t steel start to lose its temper around that temperature?
    – MaplePanda
    Oct 27 at 8:24
  • @Michael if you absolutely must use threadlocker.... just use the low-strength "hand" version. We're talking about bicycle levels of torque, not bulldozers. I'd worry that you're masking another problem though, perhaps worn threads?
    – Criggie
    Oct 27 at 8:53

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