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13Mm Wrench Nuts


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For the old timers every time you put on a flanged joint if it is a header or an intake the bolt is usually an 8mm.  The old timers also know that for that bolt there are different size nuts.   The standard size uses a 13mm wrench.  But you can also get 12mm and even 11mm wrench size nuts.  On flanges in particular the stud is by design very close to the tube so that the flange won't be put into too much bending and the clamping force will be more directly on the gasket. 


When the wrench clearance isn't there consider going to a smaller size nut.  If you do, a hardened steel washer is a good idea as it will give the reduced size nut (particularly an 11mm) a good surface to press on and not just the thin ring around the flange hole that the reduced size nut produces.  I have even ground a hardened washer to have a flat side to fit up against the tube.


Have fun

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Grinding a hardened washer to fit a side-clearance intrusion is a great tip. Had not thought of that. There are also 10mm head nuts for 8mm studs, generally referred to as Jet Nuts or K-nuts. They are all-metal self-locking nuts. Not cheap, but great for tight applications such as intake and exhaust manifolds.




--Fred '69 & '74tii

Edited by FB73tii


'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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Jet nuts have been around a long time....


For headers, I found that the guy on ebay selling deep 11mm copper/brass nuts was...




the nuts.


They work well, don't gall, and the smaller size really does help.  They're tough enough to 

not mind being pretty darned tight.


It's an aircooled VW thing, too, I guess.



"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Another trick for both (cast iron) exhaust manifold nuts and the clutch master cylinder nuts:


Check clearance for a socket or box wrench; if it's insufficient (and it will be for certain exhaust manifold nuts and both clutch M/C nuts), before installing, grind a little metal off the offending part until you have clearance.  Both the manfold and the M/C casting have plenty of metal; you're not gonna weaken 'em with the small amount you're removing.  Makes reinstallation (and subsequent removal) much easier.



'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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