140 Manifold studs

I'm looking to replace my manifold studs but can't find anything long enough. Standard is 5/16" x 45mm(probably 1 3/4"), both sides UNC. Almost every stud I can find is UNC in the head, UNF outside.

I'd be happy enough to fit the UNC/UNF other than I need to remove the studs to remove the headers, which means double nutting them each time. I've got loads of 5/16" UNC nuts but UNF ones, less so. And I don't want to have to carry both lots of nuts in the spares case.

The ideal stud would probably be 2" with an allen key head so I can R&R the studs easier.

Any suggestions?


  • Have you visited any businesses that specialise in fasteners? You'll probably want a grade 8 or grade 10 bolt that you can cut to the required length. Otherwise get a longer threaded bolt and cut the head off to make a stud (or all-thread).

    The main reason for using studs is that the insertion length into the head is known and fairly constant, alignment of the manifolds is easier and the stud will come out of the cast iron head if the nut on the end seizes up.

  • Hi Ian,

    I'd looked locally and also with Summit Racing that I've always found good. Either too short (rare) or the UNC/UNF combo (common).

    I was looking for a stud rather than just cutting a longer bolt down to be able to have the unthreaded part for the manifolds to sit on.

    I can get them from the usual suspects (IPD, Scandix etc) but they are usually 45mm and I'm trying to get something a little longer because of the thickness of the flanges on both my header and inlet manifold.

  • Have a look at the Ford Mustang long exhaust studs. Summit may have something like the long ones in this link:


  • The shorter ones look good and like the ones in the ‘might also like below’. I’ve emailed them for dimensions.

    i also see bolts for a Mustang in the ‘might also like’. Not sure why they’d use bolts although access might be an issue. I remember on my old ‘73 Corvette that access in that area was a real pig.

    Bolts might actually be better for my use since I need to remove the studs to get the extractors off.

  • The Mustang ones turned out to be 7/16", so I'm still looking.

  • 242GT242GT @242GT Wollongong NSW

    When I rebuilt the 144 race car head I converted the bolts to 10mm studs bought from local nut & bolt supplier.

    Just needed to enlarge gasket holes and die grind some extra clearance here and there.

  • 242GT242GT @242GT Wollongong NSW

    I've seen 3/8" eh holden head studs used as well.

  • 242GT242GT @242GT Wollongong NSW

    You can see the 10mm studs in this photo.

  • 242GT242GT @242GT Wollongong NSW
    edited December 2019

    By converting to the 10mm studs that are readily available you increase the shear strength diameter of the stud and reduce the risk of over tightening and either stripping thread or snapping the stud.

    A 10mm nut can be easily sourced if you drop and loose one.

    And by luck alone the existing diameter of the 5/16" hole suits the 10mm taping size.

  • I'll be back at the car at the weekend and will check it out. By 10mm do you mean an M10 thread?

  • 242GT242GT @242GT Wollongong NSW

    Yes, 10mm thread, it's a finer thread than 3/8" but almost same diameter.

  • What's your view on 10mm vs 3/8"?

  • 242GT242GT @242GT Wollongong NSW
    edited December 2019

    140's are imperial if your a purist go 3/8" diameter, 10mm is available every where around Australia.

    I liked the fact that the larger diameter stud allowed you to apply more than enough torque pressure to seal the gaskets without stretching or snapping the thread or stud.

    You'll probably find that 8.8 grade 10mm studs and nuts cheaper and easier to find in say 50mm long.

    Use a thick 8.8 flat washer with a 8.8 spring washer.

  • 242GT242GT @242GT Wollongong NSW

    Expand the photo and you can see how the 10mm diameter x 50mm long fits the manifold and extractors on

  • 242GT242GT @242GT Wollongong NSW

    Same here with the extractors with metric stud

  • I'm running webers with a KG Trimning header. The headers shouldn't be a problem but the weber manifold is tight on the studs. I'll need to do some measurements to see if it will all fit with the bigger studs. The arguments in favour are very persuasive.

    FYI, we broke a manifold to weber stud on the Peking to Paris rally, which leans me to stronger studs everywhere. Damn the weight!

  • 242GT242GT @242GT Wollongong NSW
    edited December 2019

    Drill the webber manifold & header holes out to a loose 10mm fit. It's an increase of 1.5mm from the original 5/16" diameter or 0.75mm on the radius.

  • Damn, I've just had the headers ceramic coated!

  • 242GT242GT @242GT Wollongong NSW

    You may still be able to enlarge the holes by .75mm on the radius without any damage , soumds like it will be very nice once its finishedI was just looking at a green 145 down at the mechanics yday.

  • The car is already finished. I'm just refreshing it after a very long, hard rally. We didn't snap any head manifold studs, just the manifold to carb one.

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