Ultimate thread repair guide. (And how to prevent)


New Member
Jun 28, 2021
The Netherlands
Thanks for the info.

I have a few questions.

Which primer to use?
Is there a contact resistance using locktide? Do I have to tension the bolt to get a low resistance or can I leave the stud in it while curing?

Frank in Thailand

making mistakes so you don't have to...
Feb 17, 2020
Hi @Blue-Flower , welcome to the forum!

The name primer is perhaps misleading.
Better name is activator, 7471 and 7649 is mostly used.

Attached the Loctite user guide
( @ArthurEld The RTFM ) and overview of the different primers and activators.

I used 7649 (activator) and 263 (Loctite Red)
(main overview picture shows my 770, that I use for superglue priming.... Oeps..
I didn't use that for the threads :). )

Your question:
Is there contact resistance using Loctite?

Is already answered in this thread.
Yes, anything you use that isn't metal (or graphite) is "non conductive" epoxy or Loctite will reduce the conductivity, aka increase resistance.
Lucky we don't need the current contact flow via the stud, but the aluminium and bus-bar surface.

With the bus-bar in place, washer and nut, the stud will receive voltage as it goes from the aluminium to bus-bar, to the washer and nut to the stud.
The studs still can be used for Voltage readings or BMS.

Your last question seem to be 2 in one?

"Do I have to tension the bolt to get a low resistance or can I leave the stud in it while curing?"

- Do I have to tension the bolt to get a low resistance.

For the Loctite or epoxy, it doesn't matter as it's all more or less "non conductive" (there is high priced alterative to Loctite Red, that is conductive)

In general, absolutely!
That's what makes the contact.
For M6: 3.5-4Nm torque is advised, no more then 7Nm Torque as that might twist the terminal in its plastic holding... And you absolutely don't want that
I do my contacts 4.5Nm, to be sure.

- or can I leave the stud in it while curing?
Absolutely necessary to leave the stud in.
Isn't that the whole purpose??

Except for the Loctite thread repair.
That one uses release agent and needs to be screwed out after 5 minutes.

Loctite Red needs normally 24 hours to fully cure.
With activator this should be a lot shorter, like 30 minutes.

There are probably 10.000 different visions on what that 24 hours is interpreted.

In car repairs, you clean the surface, apply Loctite, and mount with full torque as you where supposed to do, just not stress the contact within 24 hours.
It's used as locking agent not to strengthen the bond, but avoid self release of the bolt/nut due usage, vibrations and heat.

For us, we don't care about it's locking agent qualities, but it's bonding strength with the weak aluminium thread.

While end result is the same: it's almost impossible to unthread a stud/bolt that is probably connected and cured with Loctite, our useage is different.

For us:
It's to increase the bonding to all the aluminium surface inside the threaded hole with all the surface of the stud.
With this increased bonding, we can apply (a lot) more torque without pulling out the stud, and apply enough clamping force to have optimal contact between the aluminium terminal surface and bus-bar.
Without "help" from Loctite or epoxy, several brand new first time mounting threads won't hold the needed 3.5-4 Nm... And mounting -remounting several times is killing.

When you twist in the stud, almost all the way down, you can wiggle it a bit, and move up and down... there is some space between the threads in the aluminium and the threads on the stud.

High quality threads on bolt/nut (or hole) have minimal wiggle space, almost none.
A really tight fit.

Lower quality is pre-production studs/ bolts / nuts found in general hardware store.
When you order online, that is probably what you are going to get.

Most threads in the terminals are cut, not formed, as it's quicker, and more easy to do.
Besides forming tap is 10 times more expensive then cutting tap....
(Forming tap threads are a lot stronger)
As it's not precieze engineering (backroom China "Factory" with drill press and hand tap) the thread quality in the terminals are low, and sometimes skewed..

High quality studs will already decrease the wiggle room.
(And increase total contact area)

@Just John told me that higher quality studs are available in USA at "McMaster Carr"
Standard are roughly 100 for $10 (stainless grubscrew)
quality are 10 for $3.50

For Loctite Red, it's easy to apply and with the correct primer should give just about the same strength bonding as quality epoxy.

It's not made to fill larger gaps between (really badly made or damaged) threads, that's where epoxy should help.

Epoxy is a lot more hassle to do, compared to Loctite.

Most hassle (staining release agent, and harder to clean after applying) was the Loctite thread repair, but it does give high quality thread to thread contact.
I'm not sure how it will hold-up, strength wise.

It was easy to apply and almost liquid.
As I wanted to follow the manual, I used the release agent.
That step isn't needed (!!)
It could be used as normal epoxy, with the benefits of epoxy (fill larger gaps) and (almost) the speed of Loctite Red.
Price $22.50 Vs $8 or so for quality epoxy.

I can suggest to apply some grease on the aluminium to more easily remove the excess blue epoxy.

Ox-gard works great, and it's almost mandatory to use antioxidation compound like this to have long lasting quality contact within corrosion problems.

Long reply, I hoped to have answered your questions.


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Swears he didn't start that fire.
Sep 12, 2020
Just to add...

I used Loctite 263 on my threaded stainless rods that go into my cells. I used a drop or two on the threads of the rod then put them into the aluminum terminals. They hardened very well and have been in service for about a year now with no issues.

Frank in Thailand

making mistakes so you don't have to...
Feb 17, 2020
Just to add...

I used Loctite 263 on my threaded stainless rods that go into my cells. I used a drop or two on the threads of the rod then put them into the aluminum terminals. They hardened very well and have been in service for about a year now with no issues.

I don't doubt they are in service long time.

I do doubt "they hardened very well", with a good bonding to aluminium and stainless steel.

Did you try to release them?
You should absolutely not be able to!!
Or, strip the aluminium with it.

Just "for the fun of it", I did a few threads without primer.
Some are stuck tight, with the amount of force I dare to give (and I'm not gentle) it stays strong inside.

Some can get turned out.
Something that should be impossible without heat, 250c, much more then the terminal can handle..

2021-7-3 12-20-27.jpg

Nice powder, so the Loctite did harden, and almost clean stainless steel grubscrew....
= Bad adhesion to the grubscrew.
2021-7-3 12-25-3.jpg
Also released from the aluminium...

I doubt I need to say more.

Perhaps people use Loctite for the first time and don't know how strong the normal bonding is with iron.

To get an idea:
You will usually break the bolt before the Loctite bonding releases.
The heat is absolutely necessary to unscrew.

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Frank in Thailand

making mistakes so you don't have to...
Feb 17, 2020
Update !!!

Time enough (since June 26) for the epoxies to harden, and even Loctite without primer...

I already gave the "spoiler" with Loctite without primer...
It sure does help a little, absolutely not what it can be, for strong bonding.

I don't feel like pulling +10Nm on a good contact, to pull out the thread/grubscrew with good Loctite contact, but perhaps I have a bad cell that can be sacrificed.

The removed threads that where normally in need for helicoil upsize (M7 thread), that I tried to fix with the several epoxies.

On M6, all failed. :-(

After 3.5 Nm, I can feel them letting go.

I didn't twist the same after releasing, some you can see threads inside, chunks, or total smooth released.(Marine)

2021-7-3 12-15-58.jpg
JB Weld

2021-7-3 12-16-5.jpg
JB Marine Weld

2021-7-3 12-16-23.jpg
Devcon plastic steel epoxy

2021-7-3 12-16-50.jpg
Loctite thread repair

JB Marine Weld is the strongest bond, the other 2 are the same.
One release at 3.8Nm, one is still in use, @4.3Nm no problems.

For the quick hardening Loctite thread repair, released at 3.8Nm.
Impressive, compared to the other 3, who need +24 hours to harden and this is supposed to be fully hardened in 30 minutes..

For many setups, 3.8Nm is sufficient.
3.5Nm also might be doable, especially with a smaller bus-bar, who will have more pressure on the available surface.
I use Bus-bars that fully cover the the whole terminal, more contact area, also more torque needed to get the same clamping force per mm2.

On M8, Loctite thread repair holds perfect, even @5.0Nm

The threads that where damaged, I've shown several pictures, where some thread is still available, not enough to hold the +4Nm Torque I like to give, as I could feel them slide, and max 3.2Nm..

You will know when you have one...

Don't keep applying torque, and pull out the whole thread!!
(I never did, still had a few totally smooth M6 walls)

With a bit of luck, unscrew the stud.
Remove lost aluminium chunks or spiral.

And apply epoxy!!!
All my 4 available USA epoxies held up great!

Again, I don't feel the urge to keep applying more force to see when they release, 4.2Nm still feels solid.

Perhaps I have a bad cell that can be sacrificed... For now...
Not with M6.

M8 is "different".
Not only is the stud bigger, it has different thread, 1.25mm per turn Vs 1mm for M6.

Where M6 has some "sponge" area, torque builds up more slowly, M8 suddenly "hits bottom" and often is on 5Nm Torque without effort.

I didn't have a Torquemeter when I started.
It might be healthy clean, fresh and quality M6 threads have no "sponge" feeling when tighting.
To long ago, I don't remember.

I can tell that if you mount and re-mount several times, it will get some "sponge" area, about 1, 1.5 turn before you really see/ notice increase in Torque.

Some people might say that M8 is bad, as you lose quite some aluminium and copper contact surface.

Thrust me when I tell you, it's more then enough!

Standard bus-bar from China cover only partly the terminal.
Bus-bar for M8 cover just as much, perhaps more.

Besides this, you can apply more torque, 4.5-5Nm without issues.

I even dare to say that M8 will have better contact then M6.
2021-7-3 13-9-4.jpg
M6 grubscrew and standard 2mm Bus-bar

2021-7-3 13-9-40.jpg
My home made M6/M8 bus-bar (4.5mm thick)
(I also use for M6, with 6.5mm hole)

250A is not a problem :)
Should be able to withstand over 500A, a load I will never get.

I oversized to reduce heat, at extreme high loads.
While Loctite (with primer) doesn't reduce in strength up to +200c,
Most epoxies start to get soft at +60c, 150F

60c isn't a lot
And the epoxy is the trick that keeps many Bus-bars clamped tight with +4Nm torque.
In other words, there is a constant pulling force on the epoxy.
Getting it soft is BAD!!

Why epoxy at all?? Why not all helicoil??

Mostly as the work needed for helicoil, the risk that it goes wrong, upsize to M8.....
If I can avoid, great!!

I have 32 cells doing now all the work, several with cheap Thai epoxy, that for some lucky reason does stick strong enough.
After several months, all contacts are still OK.
They don't get warm :).
(Good contact, large enough Bus-bars)

Thailand (our area) reach 44c on regular basis, 47x is the max I've seen.

That's a small temperature difference to +60c....
Luckily, I have them in a special fire "proof" closet, with automatic human safe fire distinguisher, in our bedroom, and they are cooled with the airconditioning from the bedroom.
Temperatures stay below 40c.

My BMS (DIYBMS V4) has 2 temperature sensors per cell module, one for the module (dumpload) and one for the cell.

I have 2 different versions,
4.2 and 4.4.
1.2 and 1.5A dumpload per cell module :)
WiFi, database integration and much more goodies.
2021-7-3 13-33-54.jpg

That all folks.
If I have defective cells to test M6 Loctite with primer, I'll update!!
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