I've posted this before, but I pull it out when loctite discussions start going the way of color alone. FWIW.
271, Red: High strength threadlocker for larger diameter hardware.
262, Red: High strength threadlocker for for hardware smaller than that which uses 271 (more like heli parts). Either does a good job for our stuff, however. I see 271 most commonly in auto parts stores.
609, Green: Retaining compound, high strength, for mounting slip fit bearings to shafts. An appropriate product for tail boxes.
603, Green: Retaining compound, high strength, similar to 609 but good where the parts may be a little oily. Good for mounting oilite bushings in housings, BTW.
640: Green: Retaining compound, high strength. Similar to 609 and 603. Lacks the oil tolerance of 603. I use it where I might have trouble with adjacent bearing contamination with the product, such as start shaft bearing blocks, since it has a little greater viscosity than 603.
638, Green, rather thick: Ultra strong retaining compound for assemblies with a marked amount of slop in the fit, min 0.004". Don't try to use this stuff for our normal bearings on healthy shafts. It sets almost immediately in the tight gap, and you'll never have the chance to get the bearing into place.
290, Green: Wicking product for thread locking AFTER assembly. Medium strength, much stronger than 242 blue in my experience. Not the correct choice per loctite for bearing mounting.
242, 243 Blue: Classic medium strength threadlocker for most of our threadlocking applications. 243 is the oil tolerant version.
222MS, Purple: Low strength threadlocker for small diameter or otherwise delicate fasteners.
NEVER choose a loctite product by color alone.
You can build a really good model with 242 for thread locking parts you'll need to remove, 271/262 for screws you really don't want to ever move on their own, and 609/603 for fixturing bearings to shafts. 290 is great for set screws which needed to be tweaked for ideal postition of the part on a shaft (like a bevel gear) and which you don't want to have to go back and remove the screw to apply the loctite.
I know guys use other products for these tasks, but these recs are based on the specs and technical data sheets published by Loctite.