Nut size for exhaust headers

[sapstar]

Can someone please help me with this? I am quite new to DIY on a motorbike. I need to replace the rusted nuts on my exhaust and looking to buy the recommended brass nuts.

As the nuts take 12mm sockets, I assumed it will be a M12 and ordered some. These are too big. What size nuts I should by for 12mm sockets? On checking online M7 is 11mm and M8 is 13mm... But can't find what 12mm is.
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First/Current Bike - Kawasaki ER-6N

[A100man]

MOst exhaust studs are M6 and generally take a 10mm spanner.

Note that thread size (M...)doesn't automatically dictate the head size.
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Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[sapstar]

[sapstar]

I have called fowlersparts and they told me this is what I need. It says NUT 8MM. Does this mean M8?

https://www.fowlersparts.co.uk/parts/view/92210-1114
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First/Current Bike - Kawasaki ER-6N

[A100man]

[sapstar]

[Fat Angry Scotsman]

https://www.accu.co.uk/en/flanged-hexagon-nuts/409656-HFFN-M8-A4
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PRESENT: 2018 BMW S1000XR SE Sport.
PAST: 2009 Kawasaki ER-6F. 2021 Zontes ZT-125U.

[Pete.]

You want M8 nuts for 12mm hex. Exhaust studs are never fine thread so just standard ones will do. If you can find them in brass even better, in bronze even better again.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[WD Forte]

There's often confusion over bolts etc where someone will say
'whip out that 10mm bolt' when its actually an M6 bolt with a 10mm head
A lot bikes use 8mm heads on 6mm bolts too
My M8 exhaust studs have 13mm nuts just to add to the confusion.

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bikers smell of wee

[Pete.]

Never seen a M6 nut with a 8mm hex, it would leave only 1mm of metal from the thread root to the nut flat.

13mm head is standard for a M8 nut (except flanged) but not on most bikes. Typically they are 12mm hex.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[A100man]

[sapstar]

Thanks everybody for your inputs. I ended up ordering the stainless steel ones on eBay this evening. I don't think clearance for the nut will be a problem. I checked that there is enough space for an additional 1mm.

Not sure why the manufacturers can't use higher grade nuts that don't rust...
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First/Current Bike - Kawasaki ER-6N

[steve the grease]

Don't you just love the metric system. Much better than the old imperial system - everything is standard.

Sizes commonly used on bikes.
M5- everyone uses an 8mm hex
M6- everyone uses 10mm hex ( except engine case bolts 8mm)
M7- Only the french use M7 - with an 11mm hex ( makes a good replacement for stripped 1/4 bolts.
M8 here the wheels start falling off - Japanese stuff uses 12mm hex, European uses 13mm hex.
M9 - Only the French again, they use a 14mm hex.
M10 - Japanese depart from iso and use a non standard finer thread with a 14mm hex European stuff uses the iso standard pitch and a 17mm hex.
M12 Japanese, again a finer thread and a 17mm hex Europeans stanadard iso and a 19mm hex.
And so it goes.
Whilst I'm on the metric system what group of fucking idiots decided to use the same unit to measure the height of a kitchen worktop (900mm) and the thickness of a human hair (0.01mm approx) and loads of decimal points, no risk of errors there then.

At least in imperial you have cosy fractions like 5/16 that you can easily read off a ruler and if you require more accuracy theres thousanths of an inch - so 0.3125 for example
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All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....

[Pete.]