The Rest of theThreadlocking Story
Dec 25, 2018
I promised a week or so ago to add a few more tips on properly using Loctite and other threadlocking adhesives. We universally call them "Loctite," but Permatex, 3M and other manufacturers make equally good threadlocking products.
Threadlockers made by the major manufacturers come in three colors/strengths: Purple is low-strength, designed for bolts 1/4" and smaller in diameter. Blue is medium-strength, designed for bolts from 1/4" to 3/4" in diameter, and can be disassembled with hand tools. That's compared to red threadlocker, designed for bolts 3/4-inch and larger, and which is considered permanent and cannot be disassembled with hand tools. Heck, a lot of the time you can't disassemble fasteners locked with red threadlocker if you use power tools. If you use red threadlocker, consider it "welded."
If you MUST disassemble something glued with red threadlocker, use a torch or directed heat to temporarily melt the plasticized threadlocker. You'll still need plenty of "oomph" to break loose the nut or bolt because it's probably torqued pretty tight, but once it's broken loose you'll be able to remove the fastener as long as it's hot/warm enough to keep the plastic liquidified.
A final color/strength of threadlocker is green threadlocking adhesive. Green is a low-viscosity threadlocking adhesive designed to wick into the threads of an assembled fastener assembly. If you forget to put blue threadlocker on a nut or bolt, but want to ensure it won't loosen due to vibration, you can put a few drops of green threadlocker on the edge of the threads. It will wick into those threads and create a bond that manufacturers say is 1/3- to 1/2 as strong as blue threadlocker applied before assembly.