I have used several types of Locktite thread locker at my job.

222    Pink     Used on threads under 6mm          Removable by mere mortals
242    Blue     Used on threads 6mm and over       Same as above
295    Green    Will wick into threads already     Hard to remove without
                assembled                          profane language
609    Red      When you don't want to take it     You'll need a torch
                apart ever again                   to take it apart

Hope this helps.