I have been using Loctite products for decades and have never had a fastener loosen up with this stuff applied to it correctly. Not once! Click image to enlarge

Loctite® Threadlockers

Preventing things from taking themselves apart

Text, photos and video by Tom Hintz

Posted – 8-16-2011

One of the frustrating truths about anything mechanical is that vibratory gremlins within can mysteriously cause fasteners to loosen up. Sometimes the offending vibrations can be nearly imperceptible yet they seem to possess a disproportionate ability to shake correctly torqued fasteners loose. I am sure that there is a scientific explanation for how this happens but nothing can make sense of how those gremlins know precisely when it would be most embarrassing for a part to loosen up or fall off altogether. The good news is that we have weapons with which to fight these dastardly forces in the form of Loctite® Threadlockers.

The Basics

Simply put the Loctite® Threadlockers are a specially designed fluid that is applied to the threads before the fastener is assembled and torqued. While the Loctite® Threadlockers prevents loosening by vibrations and shock they also help protect the threads from rust and corrosion.

The Loctite® Threadlockers fluid is distributed over the threads as the fastener is assembled. That tiny space between the threads confines the Loctite® Threadlockers and essentially deprives it of air which is the condition in which the Loctite® Threadlockers cure. They dry in about 10 minutes but reach full cured strength in 24 hours.

The Loctite® Threadlockers are actually a family of products that help secure fasteners. There are two primary types that are common to the home DIY’er/metalworker with a third that also has a somewhat smaller utility in our market. In this review we look at the “Blue” and “Red” varieties, mainly because I was too cheap to buy the “Green” version and not have a use for it. Have faith, Loctite® makes the Green just as well as their Blue and Red types.

I applied the Blue 242 to the bolt as directed and then turned the nut on which also spreads the Loctite (left) over the threads. then I applied 40-ft-lbs of torque (right) before allowing the Loctite to cure for 24 hours. Click images to enlarge

Loctite® Threadlocker Blue 242® is likely the most popular for the home shop because it is intended for locking and sealing of threaded fasteners that we expect will have to be taken apart using common hand tools. Loctite® specifies using this type for use with fasteners from ¼” to ¾” which again should handle nearly all of the home shop needs. Loctite® says that Threadlocker Blue 242® is good for most fastener types including stainless steel and plated surfaces fasteners.

Loctite® Threadlocker Red 271™ is a stronger product that is meant to seal and lock threads permanently. Once cured the area where the Loctite® Threadlockers Red 271™ has been applied must be heated to approximately 500°F (260°C) to release its bond to take the fastener apart. Loctite® does not specify a fastener size range for the Red 271™ so I think that we can take the “Heavy Duty/For Large Fasteners” line on the packaging to heart.

Loctite® Threadlocker Green 290™ is also designed for locking and sealing of threaded fasteners. This version can also be helpful when working with welds with some level of porosity, castings and parts made using the powdered metal processes. The very low viscosity of the Green 290™ allows it to wick between assembled fasteners that have been tightened or torqued. This capillary action means that you can apply Loctite® Threadlocker Green 290™ to the fasteners of a completed assembly without having to remove the fasteners first. After the Green 290™ cures applying heat to the fastener will help break the bond so the part can be disassembled. This obviously could be a major problem depending on what the object is made from so care must be taken with the heat.

The chemical makeup of the Loctite® Threadlockers products means that there are situations for which they are not recommended. The packaging warns against using these Loctite® Threadlockers in pure or oxygen rich systems and they should not be used as a sealant for strong oxidizing materials, particularly chlorine. They also are not good to use with plastics, especially thermoplastic materials. The good news for us metalworkers is that Loctite® Threadlockers are good for just about everything we work with.

In the Shop

After the Blue Loctite cured it took almost 50-ft-lbs of torque (left) to break the nut free. The cured Loctite Blue can be easily removed from the threads (right) with an awl to re-use the fastener. Click images to enlarge

The package instructions say that the fasteners must be clean and free of oil and grease for the Loctite® Threadlockers to work properly. If this requirement is not simple common sense to you I expect many other things in life disappoint you as well. Usually just two or three drops of the Loctite® Threadlockers have been plenty for all of the fasteners I have used it on over the years. For smaller diameter fasteners one or two drops seem to work well. I never spread the Loctite® Threadlockers around manually but rather apply it to the threads and let it run itself down around the fastener. Then installing the nut completes spreading the Loctite® Threadlockers around as needed. The biggest problem with using Loctite® Threadlockers is almost certainly over-thinking the procedure.

I wanted to quantify the holding power of the Loctite® Threadlockers, in particular the Blue 242®. I used a ½ by 13 bolt and nut assembly and began by making sure that all of the threads were clean and oil free to be sure I was not compromising the effectiveness of the Loctite® Threadlockers. I loaded the bolt up with an oversized nut and several washers so I could torque the nut down to 40-ft-lbs against a solid surface. Before applying the Loctite® Threadlockers I measured the torque necessary to loosen the nut from the 40-ft-lbs torque. Not surprisingly it only took about 30-ft-lbs to break the nut loose. Needing less power to loosen a fastener than it took to tighten it is just a fact of life and no doubt is part of the reason the Loctite® Threadlockers are used so often.

I removed the nut, added a few drops of the Loctite® Threadlockers Blue 242® and then screwed the nut back onto the threads spreading the Loctite® Blue 242® in the process. I immediately torqued the nut to 40-ft-lbs and left it to cure for just over 24 hours.

The next day I put the torque wrench on that same nut now with the cured Loctite® Blue 242® and broke it loose. I watched the torque reading carefully and it took nearly 50-ft-lbs of torque to begin turning the nut. Remember that without the Loctite® Blue 242® it only took 30-ft-lbs to back off the nut. The additional torque needed partially explains why the Loctite® Threadlockers prevent fasteners from loosening up. But there is more.

After cleaning the bolt I applied the Loctite Red to the threads (left) and turned the nut on to spread it out. After curing for 24 hours I had to use heat (right) as described in the instructions to get the nut to break free and turn off. Click images to enlarge

Once the nut was separated from the washers it continued to need between 5 and 10-ft-lbs of torque to continue turning it off of the bolt. That 5 to 10-ft-lb “drag” continued until roughly half of the nut was off of the bolt. Only then could I turn the nut by hand then though I tried after each pull on the torque wrench. So, if something impacts the fastener treated with the Loctite® Blue 242® and manages to break it free from whatever it was torqued against, the fastener will not continue to turn off. Something will have to apply enough torque to overcome the drag of the Loctite® Threadlocker drag to get the fastener to loosen up any further.

After you take the nut off the Loctite® Blue 242® can be easily removed from the threads (internal and exterior) with an awl. That makes it easy to apply a new Loctite® Blue 242® treatment or to re-use that fastener or to use it untreated.

I repeated this test using the same bolt and nut but this time treated with Loctite® Threadlocker Red 271™. I again made sure that the bolt and nut were clean before applying the Loctite® Red 271™, torqued it to 40-ft-lbs and let it sit so that it could cure.

The next day I applied almost 70-ft-lbs of torque to the now cured nut and it did not break loose. So I used my propane torch to heat the fasteners as per the Red 271™ package instructions and then applied the torque wrench to break the nut loose. Though I used only 40-ft-lbs to tighten the nut it took nearly 60-ft-lbs of torque to back it away from the washers. Unlike the Blue 242® that added so much drag to the nut once the Red 271™ was heated sufficiently and the nut was backed away from contact with the washers I could turn it off by (gloved) hand. The threads on the bolt and in the nut were undamaged and needed just a bit of brushing to be sure they were clean for re-use.

Conclusions

The Loctite® Threadlockers are very well known and do exactly what their advertising says they will. I have been using these products for decades and have never been let down by their performance. When you are assembling something that needs to stay put, using a couple drops of Loctite® Threadlockers is the easiest, cheapest way I know to prevent fasteners of virtually all sizes from loosening up until (and if) I want them to.

With a price tag of just $6.47 (8-16-2001) per .20-Oz tube (red or blue) the Loctite® Threadlockers are as economical as they are effective. Remember that you only need a drop or two to lock down a fastener so these tubes will go a long way. Add that economy to the time and dollars they can save by preventing something from falling apart and you could easily be money ahead.

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