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The bottle cage bolts on my bike (carbon frame) tend to unscrew easily. Instead of tightening harder (I stopped at ~2Nm), which could damage the bosses in the frame, I am thinking of using threadlock on the bolts. It should be safe as the bosses are made of metal and it's not going directly on carbon. The question is: which threadlock is best suitable for this kind of job?

I have some blue one (Loctite 243), but if purple (Loctite 222) is better, I am willing to buy some.

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  • Would you prefer another alternative, like a cork washer to take some preload?
    – Criggie
    Oct 22, 2019 at 10:48
  • @Criggie on top of the threadlock? Or by itself? does it help? Oct 23, 2019 at 13:26
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    a cork or felt washer would sit around the bolt, not in contact with the thread, but binding on the underside of the cap and the top surface of your waterbottle cage. When squashed a bit, that would provide resistance to rotation.
    – Criggie
    Oct 23, 2019 at 19:19

3 Answers 3

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Loctite 243 seems like the best bet, but 222 could work.

From https://www.henkel-adhesives.com:

LOCTITE® 243 is a general purpose threadlocker of medium bond strength. This threadlocker secures and seal bolts, nuts and studs to prevent loosening due to vibration.

LOCTITE® 222 is a low-strength threadlocker that allows the adjustment of screws including countersunk head screws and set screws. Good on low-strength metals which could fracture during disassembly

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  • I am partial to the 222 as it is designed for small screws. It appears less likely to spin the threaded insert the carbon.
    – mikes
    Oct 21, 2019 at 21:35
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Blue should work just fine. It's probably overly strong for this application, so purple would be "better" here, but I've never had any difficulties unscrewing anything using blue Loctite.

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  • I guess my question boils down to this: if I use blue, will I be able to unscrew the bolts in the future without damaging the frame? I assume from your answer the answer is yes. Oct 21, 2019 at 17:16
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Without reaching out to thread lock compounds, I'd first suggest checking these first:

  1. Did you try another bolt set? Not all bolts are made to exact standards: some fit tighter, some loose, although having the same pitch and size.
  2. Did you try using thin copper wires around bolt threads? These work surprisingly well bolts under small tension.
  3. Bolts long enough?

I think threadlocker must be the last resort. Cheaper ones do not work nice, they are not easy to preserve, they'll leave some residue on threads when removed.

If you still want to use it, blue is the one to go with. (Medium). Anything lighter is too weak, I think it was designed to fill threads to make them waterproof, instead of "locking" them in place.

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