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Which Thread Lock Should I Use?

Thread Lock is good stuff but what does it do and which one should you use? This is just a basic introduction as I'm certainly no expert but someone did ask the question on a Facebook forum the other day and this was my reply. I thought I'd paste it into my blog too in case I want to link to it in the future.

There is a lot more detailed information out there if you need it but hopefully, this will provide a good starting point.

At a simplistic level, thread lock can be thought of as a superglue for bolts (I believe it is technically an anaerobic adhesive), it can help to prevent them from working loose due to vibration and can also help to form a seal. Generally, you will be better off using thread lock and tightening things to the correct torque rather than overtightening and causing damage to components.

To add a little confusion, thread lock comes in many forms so here are a few pointers.

Thread lock tends to be classified into colours, each has its own area of application.

To 'help you', manufacturers generally don't use a container in the same colour coding as the content, that would be far too easy. In fact most thread lock bottles are red, I believe that this is a marketing thing (copying market leaders Loctite) and it can easily catch you out.

The thread lock 'colouring system' works as follows;

  • Red; this is designed for bolts that are installed on a permanent or semi-permanent basis (e.g. chassis parts). It is the strongest and will be very hard to undo, possibly even needing heat to be applied at several hundreds of degrees. Think before using it and do not use it on soft metals.

  • Blue; medium strength. This is for general purpose use and is by far the most common type. A steel bolt assembled with this is unlikely to vibrate loose but can be undone without excessive effort.

  • Purple; the lowest strength and designed for use on soft metal or alloys which may be damaged if excessive force is applied in order to undo them.

  • Green; low-viscosity (runny) and for use where gaps need to be filled when assembling threaded components. Generally a medium strength.

On top of this, some thread locks have a higher oil tolerance than others. Sometimes it is it wise to clean or even degrease bolts prior to assembly but obviously this is not always possible or appropriate so you may wish to consider different threadlocks for different jobs.

Then we have curing time (how fast it sets). Most are 'usabe' in about 20 minutes and reach full strength after about 24 hours but there are faster drying options out there.

Solid or liquid? a majority of options are in liquid form but there are some like a soft glue stick. Some of the 'hard' ones can be applied to bolts and will not start to cure until tightened months or even years later (bike brake rotors are often supplied with bolts treated with this). The majority of thread locks will be supplied in liquid form.

How much should you use? typically 1 or 2 drops will be about right for each bolt, make sure any excess is wiped off after use but avoid using your fingers to do this as it can be bad for the skin and serious if you get it in your eyes (it also kills fish).

So, going back to the original question, which should I use? The best known brand is Loctite, their medium strength liquid for general use is Loctite 243 which is also moderately oil tolerant making it a good 'all-rounder'. This is my 'go to' thread lock and has never let me down get.

Hope this helps.

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