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.