Loctite Threadlocker Series: A Full Guide

by | Comparisons (Tools), Home Improvement

It’s frustrating, isn’t it? I love Loctite products, but navigating through their catalog is pure hell. It’s like a labyrinth.

Well, I decided to write this short guide and help you out.

I’ll look at three Loctite variations:

  • Loctite Blue (medium strength): 242 vs 243

  • Loctite Red (high strength): 272 vs 271 vs 262

  • Loctite Purple (low strength): 221 vs 222

If you want to know more about any others, let me know in the comments.

Medium strength series:
Loctite 242 vs 243

My recommendation: Loctite 243.

Both the 242 and 243 are from Loctite’s so called Blue product line (medium strength). You’ll use them to prevent any fasteners from getting loose from vibrations or experienced shocks. Both share the following common properties:

  • You should use them with 1/4″ to 3/4″ bolts

  • Their temperature range maxes out at 360°F

  • You can remove them with standard hand tools

The big difference?

Loctite 243 comes with significantly improved oil tolerance. Even if your threads are a little dirty and oily, it’s not a big deal. No need to use any primers on plated fasteners either.

If you work with a tube of Loctite 242 you will have to clean all threads properly if you want the Threadlocker to work at all.

Sure, it seems like a very small difference…However, things get sticky and oily all the time! I do appreciate the time-saving side to the Red 243 Loctatite.

Loctite 242 vs 243: A good reason why the newer 243 threadlocker is better

Now, some people say that the 243 is also just a little bit stronger. Honestly, I’m not sure about that. I consider them the same in terms of strength.

By the way, fixture time for both is only 10 minutes; full cure comes after 24 hours. These work great with steel or stainless steel, as well as most plated fasteners. Decent anti-corrosion tolerance and mild resistant to most protection fluids too.

High strength Threadlocker series:
Loctite 272 vs 271 (and 262)

OK, so here we have quite a few differences and I think the best option would be a quick comparison chart.

As a preface: these are Loctite’s Red threadlocker line. If you want to remove them, you’ll have to use heat and sweat a bit over your hand tools. They’re pretty hardcore.

Thumbnail 271
  • Loctite 271
  • Fastener size:
    3/8" to 1"
  • Maximum heat:
    300°F
  • Fixture time:
    10-20 minutes
  • Example uses:
    Press fits, shock absorber mounts, wheel studs
272
  • Loctite 272
  • Fastener size:
    3/8" to 1 1/2"
  • Maximum heat:
    450°F
  • Fixture time:
    40 minutes - 1 hour
  • Example uses:
    Crankshaft bolts, shock bolts, ring gear, idler bearings
262
  • Loctite 262
  • Fastener size:
    Up to 3/4" bolts
  • Maximum heat:
    300°F
  • Fixture time:
    Around 10 minutes
  • Example uses:
    Ring gear, transmission shaft bolts, cylinder block bolts

In other words, the 272 is the most heavy-duty adhesive here. Both in terms of heat resistance and supported size of your fastenings.

All of these cure fully at the 24-hour mark.

Important note: Do not confuse Loctite 262 with the Loctite 2620! 2620 is harder to find and is the brand’s most heat-resistant beast yet. It goes up to 650°F!

This series is perfect for more heavy-duty automotive use, like keeping those shock mounts tight.

Low strength series:
221 vs 222 Loctite Threadlockers

Finally, we’re coming to the purple Loctite series. These are perfect for general use and extremely easy to remove after application.

Is there a difference between Loctite 221 and its counterpart – the 222 Threadlocker?

Very little.

They’re actually interchangeable as far as I know. We’re talking about low strength, low viscosity adhesives for small threads. General household stuff or very low torque stuff like scope mounting are perfect usage here.

The only slight difference is that the breakaway torque on 221 is 8.5 newton meters. It’s 6 newton meters for the Loctite 222.

Otherwise, both of them share the following:

  • They work with small screws under 1/4″

  • They withstand up to 300°F

  • Fixture time is quite fast – 10 minutes, sometimes even less

As other Loctite threadlockers, the full curing time comes after 24 hours.

Whew! I think I covered the most common Loctite threadlocker types: Blue vs Red vs Purple. I hope this was both easy to understand and explanatory enough for you!

As I mentioned, if you want me to cover any other Loctite series or add some complementary information – let me know!

Founder of ToolingFun. Couldn't even change a lightbulb in my teenage years. Discovered the joy of DIY projects during my 2nd year in college. All about tinkering around, trying fun tools and projects, and giving my opinion on industry brands!