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Discussion Starter · #1 ·
The end nuts on the front ARB's on my car have a UNC thread on them. I imagined everything on the Saab would be metric!

I went to get some new ones, since they are nylock, and that's when I found it out. So the new ones they've given me are an imperial size.. 1/2" or something.

I took the old ones off with a 16mm spanner. Should it have been 5/8" instead?
 

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Discussion Starter · #3 ·
Hmm I think you are right Daz, or nearly right. It's a coarse thread, which I suppose is why the fasteners guy thought it was UNC. I went to see one of the guys in the drawing office at work. He says 1.25 is the standard pitch for that size, and he reckons it's a trapezoidal 1.5mm thread - TR8x1.5. That would be special order at any supplier, so it's either off to the dealer, or out with Loctite. I wonder which it will be?
 

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If it was UNC it would be coarser than Metric so that should count it out. Rule of thumb - if the insert is blue Metric, if it's white Unified, red BSF/Whit, yellow BA. Doesn't alawys work but should generally be true. Also check the height to the shoulder of the nut as they often use type T Nyloc's rather than a normal type P (forget the DIN numbers). If it's standard metric fine you should be able to pick one up with reasonable ease from any decent fastener distributor.
 

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Only had my wishbone off on saturday to do the butterfly bush at the rear (MOT time), I could be wrong but I could've sworn the nut that you are referring to was a standard M10x1.5mm nyloc nut.
 

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Discussion Starter · #7 ·
Thanks for all the feedback. Looks like I need to go back to the fasteners supplier and tell them they got it wrong and to try again!

Thanks

P.S. The insert is yellow
 

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You need to be very careful when trying to check nuts and bolts. A trial and error method is dangerous. Some wrong threads are obvious in that the nut will only go on a turn or two before jamming, but others will go on much further.

Some will go on about 10 turns before they jam
Which is a serious problem because most nuts don't have the length to do that and they will run the full length of the thread and so it appears than the nut fits.

You need to realise that the nuts that go on further when the wrong are just catching the tips of the thread and so not providing any real strength. This is even more of a worry on "Nyloc" nuts as they have in-built friction which can make you think it's tighter and stronger than it is.

I have a table that shows the problem somewhere. I will try and look it up.
 

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If you can, try and get your hands on the Bossard catalogue (its a book about 3 inches thick.) I worked for 10 years in the fastener industry as as a technical sales manager, QA manager plus I set up and ran the company's military and aerospace fastener division and I found the Bossard book a mine of information. Alternatively you can check it out online here:

Bossard Online catalogue

By the way I've no connection with them (plus they don't sell direct anyway) but the link may be useful.

Cheers

Ian
 
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