Here is factory description of various formulations:
Loctite 222 - Low Strength (LOC-22221)
Use Loctite 222 where occasional adjustments of small fasteners may be required. Small hand tools can be used to overcome the adhesive seal. Best for 1/4†and smaller fasteners. Temp. range: -65º to 300ºF (-54º to 149ºC).
For scope parts(ie small diameter screws) the one above might be the best. All formulations are available at industrial supply outlets AKA Mill Supply Houses and at fastner stores.
Loctite 242 - Medium Strength (LOC-24221, LOC-24231)
Make ordinary nuts vibration-proof! Loctite 242 holds bolts and cap screws securely, while sealing out air and moisture, thus preventing wear and corrosion. Nuts can be removed with ordinary hand tools. Temp. range: -65º to 300ºF (-54º to 149ºC).
Loctite 262 - High Strength (LOC-26221)
helps you permanently anchor studs, cylindrical parts, bearings and bushings. Replace shaft locking devices such as keyways and splines. Provides greater break-loose torque than Class 5 Interference fits. Seals against leakage and corrosion; unaffected by liquid fuels, lubricants and most chemicals. Temp. range: -65º to 300ºF (-54º to 149ºC).
Loctite QuickStix 248 (LOC-37684)
ThreadlockerMedium Strength/ Removable/Blue, New, patented semi-solid stick formula offers added convenience and portability. Like Loctite® 242®, this threadlocker stics is well suited for ¼†to ¾†(6 to 20 mm) fasteners and is removable with hand tools. The semi-solid formula also means it won’t spill or leak.
Loctite QuickStix 268 (LOC-37685)
ThreadlockerHigh Strength/ Red, Revolutionary semi-solid stick formula is high strength and best suited for fasteners up to ¾†( 20mm ). Semi-solid formula offers added convenience and portability. Localized heat and hand tools are required to separate parts.
Loctite 271 - High Strength (LOC-27131)
High strength adhesive for larger fasteners up to 1" in diameter. It is used with marine engine studs, automotive suspension bolts, pump fasteners and with other heavy duty bolt applications. Temp. range: -65º to 300ºF (-54º to 149ºC).
Make sure you use the right one. High or medium strength means what it says!
