Loctite 242 vs 243: Choose The Right Adhesive For You!

Are you looking for the threadlocker to apply to fasteners like bolts and screws to prevent leakage, loosening, or corrosion? The German brand – Loctite has got your back.

The products come color-coded to indicate strength and whether they are removable or permanent. Among them, the Blue Loctite is the sweet spot in terms of sturdiness. This liquid is strong enough to place the nuts in the spot without becoming too tough to remove.

So, what’s the basic difference between Loctite 242 vs 243?

Both are suitable for machine tools, pumps, presses, compressors, mounting bolts, gear-boxes, and so on. However, the 243 adhesive outperforms 242 adhesive when it comes to oil tolerance. 

Let’s go through my detailed review to know more!

What is Loctite 242?

The Loctite Threadlocker 242 refers to the all-purpose threadlocker or the ‘original threadlocker’ which is a medium-strength, medium viscosity, methacrylate-based threadlocking adhesive.

This one is utilized for valve cover bolts to carburetor studs. Loctite 242 is suitable for less active substrates such as stainless steel and plated surfaces and offers quick fixture times on steel, brass, and stainless steel of 5, 15, and 20 min, respectively.

Since it is thixotropic, it seals even when the screws vibrate and protects the threads from corrosion. And it requires normal disassembly with standard hand tools. Now you can go without the expensive lock nuts and lock washers when you have the Loctite threadlocker 242.

Some salient features of Loctite 242

  • Cure Time: Up to 24h depending on the substrate used and temperature.
  • Full Cure Temperature: 77 °F
  • Specific Gravity:07 g/l
  • Specific Gravity Temperature: 25 °C
  • Temperature: -65 – 300 °F
  • Thread Size (Maximum): R3/4″
  • Torque Break on M10 Steel: 110 in./lb.
  • Torque Prevail on M10 Steel: 43 in./lb.
  • Viscosity: 800 – 1600 mPa.s (cP) Brookfield
  • Cure System: Anaerobic
  • Flash Point: >93.3 °C

What is Loctite 243?

The Loctite threadlocker 243 is a general-purpose member of the ‘blue crew.’ It has an improved oil tolerance aspect with surface-insensitive properties. It is also a medium-strength adhesive that is based on acrylic technology. 

Loctite 243 prevents leakage due to vibrations and shock in closely fitted metal surfaces such as steel nuts, bolts, metals, brass, and copper. Don’t worry if the threads are a little dirty or oily! It can vigorously withstand high temperatures, oil contaminations, varied fluids, and anti-corrosion.

The plated fasteners won’t need a primer if you apply this upgraded version. The rocker studs, oil pans, pulley assemblies, disc brake calipers, and many more projects need the application of this adhesive.

Tip – You should not use the product in an oxygen-rich system, and this should not be selected as a sealant for strong oxidizing materials. 

A public health organization, NSF International, certifies that LOCTITE Blue 243 can be used in potable water systems with temperatures not above 82°, and it should not be used around food processing areas.

Some salient features of Loctite 243-

  • Fixture Time: 5 – 10 min.
  • Full Cure Temperature: 77 °F
  • Specific Gravity:08 g/l
  • Specific Gravity Temperature: 25 °C
  • Chemical Type: Anaerobic
  • Temperature: -65 – 360 °F
  • Thread Size (Maximum): R3/4″
  • Torque Break on M10 Steel: 230 in./lb.
  • Torque Prevail on M10 Steel: 40 in./lb.
  • Viscosity: 1300 – 3000
  • Viscosity Temperature: 77 °F

Another Tip – You should not use the product in an oxygen-rich system, and this should not be selected as a sealant for strong oxidizing materials. 

See AlsoLoctite 271 vs 272: Which Lube Is Right For Your Threadlocker?

A Detailed Comparison Between Loctite 242 vs 243

Are you getting confused about which Loctite medium strength Blue Threadlocker to choose? Check out the comparison chart before making your decision –

Features Loctite 242 Loctite 243
Type Medium strength Medium strength surface insensitive
Torque to break free (​38-16 size bolt) 115 in-lb (12 N⋅m) 180 in-lb (20 N⋅m)
Torque to continue turning 53 in-lb (6 N⋅m) 53 in-lb (6 N⋅m)
viscosity 1200/6000 thixotropic 2250/12000 thixotropic
specific gravity 1.07 1.08

Cleaning Before The Application

If you are applying the 243 adhesive, it will not be an issue if there is some dirt or oil on the threads. Additionally, there is no need to use any primers on the plated fasteners.

In contrast, when you are working with a tube of Loctite 242you will have to clean all the dirt to get a proper result. So, the Loctite 243 would not need a primer, but 242 does.


242 is a medium strength adhesive and the 243 is medium strength surface insensitive adhesive. So, the former prevents the loosing of the fasteners but can be removed with hand tools. So, the Loctite 243 would not need a primer, but 242 does.


Since you have to clean the threads for the Loctite 242, it can be time-consuming.

Oil resistant

The Loctite 243 is more oil resistant than the 242. That’s why the threadlocker 243 will be ideal for something like an oil pan or helpful for chain maintenance.

Torque break and Viscosity

The 243 comes with a higher torque brake than the 242 one. The former one also comes with a higher viscosity than the latter one.

Which One To Choose – Loctite 242 or 243?

The choice depends on your preferences and availability. These two adhesives are removable with standard hand tools on ¼” to ¾” fasteners and come with fast fixture times. Again, they cure fully in 24 hours, and the temperature range of these two maxes out at 360°F. The fixture time is 10 minutes for both. They are great with stainless steel, steel, or most plated fasteners.

However, the Loctite 243 is an upgraded version of Loctite 242. You can definitely use 242 adhesive as long as you clean the threads with isopropyl for removing any machine oil.

The 242 sealant recommends the use of a special primer on passive metals like aluminum, stainless steel, titanium, magnesium, black oxide, cad plating, zinc plating, and others. So, it may not be convenient for all, and then the 243 formula solves the problem.

Unlike the 242 adhesive, the 243 formula will adhere to inactive metals without the primer.

Why You Should Go For Loctite 243:

  • Primerless application
  • Seals the threaded fasteners between ¼” and ¾” (6 to 20 mm)
  • It works not only on active metals like brass, copper but also on passive substrates like stainless steel, plated surfaces, and more.
  • Tolerates minor surface contaminations from various oils like lubrication, cutting, anti-corrosion, and protection fluids.
  • Removable
  • medium strength threadlocker

Why You Should Go For Loctite 242:

  • medium strength threadlocker
  • Suitable for normal disassembly with standard hand tools
  • Protects thread from rust and corrosion
  • Prevents loosening from shock and vibration
  • Ideal for less active substrates like stainless steel and plated surfaces where disassembly is required for servicing.

Tip- The Loctite 242 product is not recommended for plastics, particularly thermoplastic materials. 


How to use the Loctite 243 sealant? 

Follow the steps –

  • Clean the surface by using Loctite SF7063
  • Position the bolts and apply the threadlocker on the bolt
  • If there are blind holes, apply the adhesive into the lower thread of the blind hole.
  • Tighten the nuts to correct torque

When should I use a primer with threadlockers?

You need to use the primer when two inactive metals are involved or to speed up the curing process for a faster return to service.

Final Words

These thread-locking fluids exhibit a time-dependent decrease in viscosity under shear stress. Thus they flow well over time yet resistant to short-span shearing. And among all the thread treatment applications, these medium-strength blue adhesives are most commonly used.

And as you now know the differences between Loctite 242 vs 243, it is easy to see the advantages that both can bring to you, and you can apply them with precision and quality. They both have good chemical resistance. Let me know which one you want to go for!

Additionally, since I am talking about Medium strength threadlocker blue, let me know in the comment section below which one is your favorite between Loctite vs permatex!