AR-15s

Threadlockers: A Guide for AR-15 DIYers

ar-15 glue guide

Adhesives have their places in AR-15 construction projects, and application ranges from what I think is crucially important to what I think is cautiously wise.

Because of the best-known brand name association, it’s usually called “Loctite,” which, like “Kleenex,” is a name associated with a product, but not the product itself.

These products are known as “threadlockers.” There’s also Permatex brand and others.

Again because of the common association with Loctite, there are different formulations available and each might have a unique name from each manufacturer, but they are usually referenced by their color.

Color is sort of a universal means to denote threadlocker “strength.” Each bottle of threadlocker will be color-coded to indicate its strength.

ar-15 extension tube glue/threadlockers
Always, or so I say, use some blue for the lower receiver extension tube—it’s an important AR-15 component. Even taking this part to torque spec does not ensure it won’t eventually rattle.

What Threadlocker Colors Mean

Let’s take a look at each of these colors and what they indicate:

  • Blue: a medium-duty glue that’s probably the most common. Blue means the fastener can be removed with the same hand tool that installed it. It might take a little more effort, but it won’t be stuck.\
  • Purple: a slightly lower-strength threadlocker than blue that’s formulated for smaller-diameter fasteners, like set screws. It gives up its hold a little easier than blue, which is a bonus if it’s holding small screws (which have small driver fittings).

There’s not a big difference in the effective holding power of purple and blue, just, again, that purple works best on small (smaller than 0.25-in. diameter) threaded pieces and blue works best on larger threaded areas.

Either of these threadlockers dissuades unwanted movement otherwise primarily induced by vibration. That is their job.

ar-15 carrier key
A good use of Red: bolt carrier key installation. Do this in place of staking carrier screws. Glue goes on the mating surface and also the screws.

Again, something like a trigger adjustment screw (common application) can still be turned, it just makes the screw “sticky” in a way of looking at it. These have pretty much the same effect as the nylon insert inside a nut, as is familiar to mechanics.

  • Red: Heavy-duty. Folks, this is stout stuff. Don’t use it nilly-willy, think it through. It takes a whopping lot of heat, for longer than you might imagine, to break loose (especially a larger surface area parts pairing). And when I say a whopping lot, that means it’s a good 500-degrees worth. On the other hand, whatever it’s used on is forever done, the parts are patently solidified. There are different “levels” of red from different manufacturers, but all are considered “permanent” in their applications; there are small differences in formulations based on fastener area size.
  • Green: Considered “medium-to-high strength,” while blue is medium strength, green threadlockers are ideal for preassembled fasteners (e.g. set screws).

Applied over a large area (like threads on a collar), blue or purple may well require some heat to turn loose, but a heat gun is usually adequate.

ar-15 glue muzzle
Here’s another application of Red that sure makes brake installation easy! If you chose this route, just put the glue right back against the muzzle shoulder; that’s all that’s needed.

Three Things to Know About Threadlockers

Now, in general, there are a few things to know about threadlockers, and this applies to virtually all of them regardless of strength.

  1. It is absolutely necessary to get the threads and the threaded both down to their bare metal. Use a residue-free degreaser, like brake cleaner, electrical contact cleaner, denatured alcohol.
  2. Do not shortchange or disbelieve the manufacturer instructions: it takes a FULL 24-hours to cure! That’s not “all afternoon,” or even “overnight.”
  3. Threadlockers won’t set or cure in the presence of air. You can drip a few drops on the bench and it will stay liquid until some great time passes and some evaporation occurs. Unlike epoxy (exactly unlike epoxy), threadlockers work best where there is only a tiny gap between parts. Epoxy doesn’t really work well at all unless parts have been “roughed up” — it has to have a gap to seal to get maximum hold.

This also makes excess threadlocker pretty easy to clean up and off unwanted areas.

ar-15 glue degreaser
Always (always) degrease all surfaces in contact with the glue. And! Let it sit a full 24 hours or it will not cure.

Another thing to know, and keep in mind, is that these threadlocking compounds also inhibit corrosion. A mating of steel and aluminum can, over time, effectively weld the parts together.

There are also instances on an AR-15 where a steel screw is threaded into aluminum, and other areas where these metals make flush contact.

I’m not saying to use threadlocker for this reason, but it is a validation to use threadlocker! It won’t hurt a thing and might save a day.

Applications for Threadlockers

So, where to use which, and when? Put us all together and I imagine we could brainstorm a few pages worth. However, there are a few specific points and processes in a build where I highly recommend the use of threadlocker.

The first that comes to mind is installing the lower receiver extension tube (“buffer tube”) for a rifle-stock configuration. These loosen easy, so use blue.

It’s not necessary installing a CAR-style buffer tube because these have a castle nut that’s also a lock nut, in effect, but it cannot hurt.

A drop of purple is a great detail touch for many small screws, like handguard rail screws, gas block set screws, trigger adjustment screws, and the like. It’s only a little extra effort.

Anyone’s eagerness to use threadlocker has a lot to do with experience, and if you’ve experienced loosened fasteners at inopportune moments, well, that’s what threadlocker helps prevent.

If you are among an increasing number who don’t want to stake bolt carrier key screws, and I am one of you, then red is the ticket for installing this part.

ar-15 glue heating tips threadlockers
You’ll need serious heat to break loose red. It takes a good 500-degrees, and it needs to be up there for a spell. You’ll smell the adhesive melting when it’s getting where it needs to be. Two tips: One is to wrap an aluminum foil heat shield to cover the metal surface you’re focused on, and, two, give it some time after switching off the heat source (it can take a while for the heat to “soak in”).

Some competition rifle builders use it on the barrel extension (actually gluing the extension into the upper receiver). I used to do that, but no more.

Reason? It doesn’t make a whit of difference when it comes to accuracy. Believe me, I’ve tested…

Another also competition-oriented use of red is to install a muzzle device using a minimum of torque. The idea is to eliminate the otherwise small amount of muzzle constriction that results from tightening the device in place.

Do you use threadlockers? If so, what color do you use most often? Let us know in the comments below.

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (20)

  1. I use Locktite almost daily for work assembling large and small fasteners from six inch nuts down to 6-32 set screws. I use red 272 for the large stuff or anything that does not need to come apart and Blue 242 for anything that may need to be dissasembled later some day or on the smaller fasteners,
    Usually a small drop is enough for most items, use sparingly. The use of a torch is fairly common on large fasteners for me.

  2. To clarify the role of “green” threadlocker like Loctite 290, it’s a low viscosity product intended to wick into already assembled threads as an alternative to “blue” (Loctite 242).
    Also for faster and more consistent setup you can get Loctite primer that you apply before the threadlocker to both clean the part and seed it with copper ions to trigger the hardening reaction. Although I can’t think of a specific firearms use offhand Loctite also makes some sleeve and bearing retainer products designed to secure slip and interference fit parts.

  3. As a humble hobbyist with a very small metal working workshop, I’ve made special cutting tools and custom taps and such from O1 (oil hardening) drill rod on the lathe & mill. Drill rod is of course the same stuff they make drill bits from, thus the name. I buy various diameters of it in 3 foot lengths just to have on hand. I’ll use making a custom tap for an example, like say an oddball size left hand tap that would otherwise cost a bunch of money when I only need to use it once, and/or I don’t want to special order one and then have to wait for days for it to be delivered: I’d turn a length of O1 drill rod (which comes annealed and ready to machine) down to the desired diameter and then cut the appropriate left hand threads into it on the lathe. Then I’d head over to the mill and use a small ball end endmill to mill out the straight flutes, and then clean up the cutting edges and such. Then mill 4 flats on the opposite end to finally end up with a typical looking straight fluted tap, just like you probably have in your own tap & die sets at home.

    But that tap would still have to be seriously hardened so it can cut steel just like drill bits need. So, torch it to a cherry red glow and then dunk it in used engine oil to harden. In some cases I might be able to cheat and get away with using it as is from that point, but if I am doing things properly I need to then temper that steel so it isn’t too brittle. Theoretically it is possible to make steel so hard that it becomes brittle and can far too easily break or snap on you (and it is always so _delightful_ to break / snap a tap clean off deep down inside some expensive part), so some tempering to keep a little flexibility is a good idea.

    And finally here comes the point of this entire comment: For small parts I’d then then dig out the little electric oven my wife picked up for me for $5 at the local Salvation Army store, and bake that little tap at full power 500 degrees Fahrenheit for about 1/2 hour or so. 500 degrees F, just like you’d need to reach to break loose that red thread locker on something you are trying to disassemble.

    Torching any number of steel alloys to ~500F and then letting it cool slowly could change the temper of the steel. And I always think of that when I read articles like this. Obviously people do this all the time and very apparently get away with it, and I am just a hobbyist not a qualified engineer, but I always think about how I temper drill rod steel at ~500F after I oil-quench harden it, and wonder about what all that heat could do to good gun steel. And that is why I have never used red thread locker on anything I didn’t consider to be permanent as in forever. I will repeat that I am just a hobbyist, not a proper machinist much less a highly over-educated engineer, so take that as you will. 🙂

    Just food for thought.

  4. I tried pre-applying blue threadlocker to some bolts, and I discovered what you said in this piece – it doesn’t set in air. I was trying to pre-apply it, the way you get stuff from manufacturers sometimes – they’ll send you a bolt or collection of bolts, and it looks like they put a dot of blue threadlocker on each one from the factory. Howzat work? Different kind of product?

  5. I use rockset on muzzle device and gas blocks. They say it works better than blue Loctite in those places due to the high heat associated with barrel accessories. Seems to work fine and is similar to blue just heat resistant.

  6. The green that I’m familiar with and use is called “Stud & Bearing Mount” for good reason. Significantly higher break-away torque than Red, borders on being an ‘inseparable assembly’.
    The other green that I’m familiar with is very low strength, but by design will wick into already assembled components. The Lock-tite Design Manual is a wealth of information on all of their products.

    I’ve been known to cheat the thread-locker sometimes. Like when all you have is Blue and you have some concern about being able to remove that 4-40 screw if you use it. I leave a very, very light film of oil on one thread only.

  7. I’ve used Loctite Blue for the hex-head screw on the front sight of Glocks. It holds the screw well. But it takes a little work to unscrew and clean out since the heat of the barrel cooks the Loctite formulation.

    I’ve since found a Loctite #262 that was recommended for heat-affected parts, as opposed to Loctite 620 which is recommended for dovetail front and rear sights, only.

  8. If using Red Loctite on a carrier key installation use Loctite 272. This is a high heat version of their 271 “Red” Loctite. The 272 is also preferred for muzzle brake / flash hider installations.

    The most common mistake I see is where a great many use 242 Loctite (“Blue”) for most everything. On virtually all fasteners below the size of 1/4″ 222 Loctite (“Purple”) should be utilized. Why? on the smallest diameter fasteners 242 will act like 271 on moderate sized fasteners.

  9. Don’t use thread lockers on bolt carriers stake the bolts or buy one that is assembled correctly. Thread locker is not a sealant so using it on the carrier key is a bad idea use Permatex form-a-gasket to seal your properly staked key. Crush washers will keep your muzzle device on correctly and if you think the handguard in the first picture is going too come off easy your crazy. If you torque fasteners to the right specs you shouldn’t have any problems but if you go putting thread locker all over everything your going too regret it.

  10. Question. Which threadlocker would you recommend to use for a front-end vertical grip? The vertical grip is tight when install in my ar but comes loose after a couple hundred rounds everytime i shoot it. Seems like the recoil vibration and heat does it. Kinda frustrating at this point

  11. This is a great article and one more suggestion…Purple is a good thought when mounting Scope/Rings. I have seen some shooters on the rang having to grab tools when their scope slipped loose…just a dab on the set screws…. no need to drown.

    Not a good feeling when you have a nice buck in the scope and find that the scope is loose…after you watch the deer run off after the shot.

  12. I’ve built and worked on AR style Rifles since the late 70’S and never used any type of thread locker. If things are assembled correctly and torqued, staked appropriately, non should be needed other than some self assurance for the builder. Not to mention if you use red say on the barrel nut, the heat needed to remove it I’ve seen cause damage to the then softened aluminum upper in trying to remove it. Heat can also warp fragile parts, especially while using forces needed to remove them. There should be no vibration if things are tightened correctly. That’s like using locktite on the rod bolts in an engine, which is never done, even in race engines as the proper torque is applied! Never had any complaints of loose parts! User discretion is much advised!

  13. There’s a lot more to Loctite than color. Identifying which Loctite you use by color alone is overly simplistic. There are many types of blue, red, purple green and black. All have different applications based on size of thread and expected heat encountered in the supplication. Saying to use blue Loctite really doesn’t tell anyone anything about the actual conditions It is appropriate for. The numeric identifier should also always be referenced when identifying which Loctite one is using.

  14. The general rule in my shop if you use Loctite, price starts at $100 plus labor and parts. I have used some high temp Loctite but not red or blue. Purple is good for air fittings on pipe threads. Clean parts and a good clear oil goes a long way like 3 and 1 oil. This is like everyone now has to torque scope rings screws. This a waste of money. That small L shaped wrench is all you need. On big bores, I use masking tape on the bottom ring. So the scope does not slipe. Lapping scope rings makes more sense. Find a good gunsmith and ask for help and keep your mouth shut. You might learn something.

  15. I use red on the set screws that hold the gas block on the barrel. Other than that, I do pretty much what the author suggests. I don’t have the green and purple, just blue and red.

  16. Buy a properly staked carrier. Use a crush washer and shims to properly tighten and index your flash hider. Clean and service your weapon on a regular basis.

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