Loctite is a wide range of adhesives for everything from hobbyist to mechanic to building construction to military industries including epoxies, sealants, super glues and expanding foam.  Thankfully, for gunsmiths anyway, there are also thread lockers. Manufactured by Henkel Adhesive Technologies, Loctite comes in four basic colors, at least the versions commonly used by gunsmiths:

Red

These are generally considered permanent, high strength thread lockers, designed for screws and locations where the installed item will not be removed in normal use.  If you need to remove red Loctite, it will require heating the part to a temperature greater than 550 degrees Fahrenheit.  The best way to do this is to heat the screwdriver while it is inserted in the screw head, or you can use a soldering iron held to the screw for 30 seconds or so. Loctite 263 is a standard red thread locker, while Loctite 272 is a high temperature version. Dawson Precision uses this grade of Loctite on all their rear gun sights and those with screws.

Blue

These are a medium strength thread locker, able to be removed with standard hand tools.  If the screw or other item will be removed or loosened in normal use, such as a sight that might need to be adjusted, the blue group are usually the ones you want. In general, you will see two versions of blue Loctite available, numbered 242 and 243.  243 is simply an upgraded 242 with better tolerance to oils, and would be recommended for use on firearms.

Purple

This color of Loctite is a low strength thread locker designed for small screws, such as those used on many gun sights, and can easily be removed with the same hand tools used during assembly.  Purple Loctite only comes in a single number version, 222, and works perfectly for the small screws in eyeglasses that tend to work themselves loose, as well as small screws in firearms, such as sight screws.

Green

This group is a wicking thread locker and is designed to be used on pre-assembled parts.  If you have screws that need to be locked in place but can’t or don’t want to remove them to apply thread locker, the green varieties are for you. There are basically two green thread lockers useful to gunsmiths, number 290 is a medium to high strength thread locker for smaller screws and 220, which is the high strength version.  Both of these will require heat to remove, so do not use them on parts that will normally be disassembled.

Other Products

There are some other Loctite products that gunsmiths may find useful.  For example, Loctite Retaining Compound, a green variety, is used to effectively glue metal to metal surfaces.  In one of Larry Potterfield’s Midway gunsmithing videos, he shows how he uses Loctite 680 Retaining Compound to fasten a metal shim on the pivot surface of an old Remington 1900 double barrel shotgun.  Loctite 620, another retaining compound variety, is used by Dawson Precision to fasten all front sights that are not intended to be removed and are not held on by screws or posts.