Loctite Types FAQ: Threadlockers, Retaining Compounds & Cure Times

Everything you wanted to know about Loctite (but were afraid to ask)

I review industrial adhesive specs for a living—roughly 200+ unique items per year as a quality compliance manager. Over four years I've rejected maybe 12% of first deliveries due to wrong threadlocker selection or cure-time assumptions. This FAQ covers the questions that keep coming up on the shop floor and in procurement meetings.

What are the main types of Loctite threadlockers?

Loctite threadlockers are categorized primarily by strength and removability. The three main families:

Low strength (purple): 222. Designed for small screws (M2–M6) where you need to adjust or disassemble with hand tools. Tear-away torque is about 10-20 in·lb.

Medium strength (blue): 242 and 243. The workhorses. 242 is general-purpose; 243 is oil-tolerant and works on slightly contaminated threads. Both can be removed with hand tools.

High strength (red): 262, 271, 277. 271 is the classic 'permanent' red, 262 is a lower-torque red for smaller fasteners, and 277 is for large bolts (M20+). They require heat (250°C+) for removal.

Then there's wicking grade (290): a low-viscosity green that wicks into assembled threads—great for locking already-installed fasteners. (Source: Loctite Technical Data Sheets; verified pricing and specs as of January 2025.)

What is Loctite 609 used for? (retaining compound)

Loctite 609 is a retaining compound—not a threadlocker. It's designed to fill the gap between cylindrical parts like bearings, bushings, and shafts. Typical applications: mounting bearings onto shafts or into housings, securing oil seals, and reinforcing press fits. The gap-fill capability is up to 0.125 mm (0.005 in).

I've seen engineers try to use 242 for a bearing-fit problem—ugh, wrong chemistry. Retaining compounds have higher shear strength (around 2,000 – 3,000 psi) than threadlockers because they are meant to transmit loads across the joint, not just prevent loosening. If you're working with press fits that are loose, 609 is your go-to. But if the gap exceeds 0.15 mm, step up to Loctite 638 or 648.

How long does blue Loctite (242/243) take to cure?

That's the million-dollar question. The short answer: fixture strength in 10–20 minutes at room temperature, full cure in 24 hours. But—and this is where people mess up—cure time depends on temperature, humidity, and material.

Actually, let me correct that: 242 and 243 are anaerobic; they cure in the absence of air and in the presence of metal ions. On active metals (steel, copper, brass), fixture time is ~10 minutes. On passive metals (stainless steel, aluminum, zinc, or plated surfaces), fixture may take 30–60 minutes or longer. At low temperatures (below 10°C), cure slows dramatically—I've seen 243 still liquid after 2 hours on a cold zinc-plated bolt in our warehouse during a January outage.

If you need faster cure, use a primer (Loctite 7649 or 7471) or choose 243 instead of 242—the oil-tolerant formula has slightly faster fixture on passive surfaces.

Is red Loctite permanent? Can it be removed?

Here's where the 'honest limitation' comes in. Red Loctite (271, 277) is designed to be permanent for most hand tools. But not truly permanent. It can be removed if you apply localized heat (~250°C / 480°F). We've disassembled red-locktited fasteners on a $22,000 machine overhaul by heating the nut with a torch for 30 seconds—it broke free with standard wrenches.

So don't use red on something you want to service regularly. If you're unsure, start with blue (242/243). I still kick myself for a job where I used 271 on a small motor mount that needed quarterly adjustment. Had to replace the whole bracket later.

How do I choose between 242 and 243?

I went back and forth on this for months. They look the same (both blue, medium-strength), but the difference matters:

• 242: General-purpose. Works on clean, dry threads. Best for applications where you know the surface is free of oil or contaminants.
• 243: Oil-tolerant. Passes the MIL-S-46163A test for contaminated surfaces. If your assembly line uses cutting fluids or you're working on reassembled parts that may have residual oil, use 243. It's also slightly more viscous, so it stays in place better on vertical threads.

One practical tip: I ran a blind test with our maintenance team on 20 similar fasteners, half with 242 (cleaned) and half with 243 (as-received oily). The removal torque after 24 hours was within 5%—243 performed identically on oily threads. Since then, we standardized on 243 for all routine maintenance to eliminate the cleaning step. It costs maybe 10% more per bottle but saves a lot of labor. (Should mention: if your threads are heavily greased, even 243 may fail—you need to degrease or use primer.)

What's the difference between 271 and 277? (the two reds)

People think red is red, but it's not. 271 is the classic 'high strength' for M6–M20 bolts. 277 is extra high strength for larger fasteners (M20–M36). The viscosity is much thicker on 277 to prevent runoff on big diameter threads. Breakaway torque for 271 is ~310 in·lb on 3/8" steel bolts; for 277 it's ~400 in·lb on 5/8" bolts. (Source: Loctite TDS 271/TDS 277.)

If you use 277 on a small M6 bolt, you'll likely snap the head off trying to disassemble. I've seen that failure—the vendor claimed the product was 'within spec,' but the spec was for a larger bolt. Honest mistake, but it cost us time and a fastener replacement.

Can Loctite threadlockers be used on plastic?

This is a question I get all the time, and the answer is mostly no. Standard anaerobic threadlockers (242, 243, 271) are designed for metal surfaces. On plastics, they may cause stress cracking (especially in polycarbonate, acrylics, and ABS) because the monomers can attack the polymer matrix.

If you need to lock threads in a plastic assembly, use Loctite 221 (purple, low strength, flexible) or a dedicated plastic-safe formula like Loctite 2700 (high-strength, designed for plastics). Or better, use mechanical locking features like nylon inserts or serrated flanges. Honestly, I'm not sure why some engineers still try 242 on plastic—I suspect they grab whatever is in the toolbox. A quick check of the Loctite selector guide would save them a cracked part.

How should I store Loctite products?

Most Loctite anaerobics have a shelf life of 24 months from manufacture when stored at 8–28°C (46–82°F). Keep them away from heat sources and direct sunlight. I've seen expired 242 that turned into a thick paste—it didn't wick into threads at all.

One thing I learned the hard way: never store Loctite bottles upside down or on their side. The liquid can get into the cap threads and cure there, making the cap impossible to open. (Surprise, surprise—we had to bin a whole case of 271 because the caps sealed themselves.) Store upright, and if the cap gets stuck, a little heat from a heat gun usually loosens the cured adhesive.

Oh, and check the lot number before use. If you're not sure when it was manufactured, apply a drop to a scrap metal surface and see if it cures within 20 minutes. That's the true test.