Which thread lock?

Just get the Blue Loctite 242 in a small .2 ounce tube that will cost about 6 to 7 dollars, anything else will cost you almost the same and won't work as well.

You could try using a small piece of 2 pound test monofilament fishing line, simply put it into the hole than screw the bolt in, works kind of like those nylon lockwashers you see.  

Don't use nail polish though, the chemicals in polish can eat at soft metals.

I haven't tried this because I never have it around the house, but I've heard that Karo corn syrup works, just apply a small dab and insert screw, once it dries it becomes tacky and will hold stuff like bicycle related parts.

Try the cheap alternatives first, if one works then you don't need to get the Loctite.

I find rust is an excellent thread locker and it's free.  At least initially.

Medium strength works fine. The Loctite equivalent is 243 (blue); there are similar variants. The key requirement is that the fastener should be able to break free with hand tools.

I think you may want the high-strength stuff for places like press-fit bottom brackets.

Blue paste version does for 99% of jobs

I got mine from toolstation, £2.63.

https://www.toolstation.com/shop/Plumbing/d20/Plumbing+Consumables/sd271...

Works for me.