Which threadlock on bottle cage bolts? 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.
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