Manifold studs

I can’t seem to work this out, tried counting threads etc etc...does anyone know the thread for the manifold studs on an alloy head? I’ve got the studs out but need different length ones for a new set up. I seemed to measure 20 threads per inch which would say 1/4” UNC but appears most sellers only do 3/8 or 5/16” studs which makes me think I’m getting some thing wrong here. Any help much appreciated ta
 
Do you have or know some one with an imperial tap and die set? My metric one has a pitch gauge set (like a toothed feeler gauge) to measure the thread
 
I would guess they would be 5/16 UNC as 1/4 seems too small. I've not long bought some for the mini and they were 5/16 UNF (fine thread for iron head) so I cant see your ones being any smaller. A bit of a shot in the dark I know but it's the best I've got.
I could try measuring one tomorrow if you can wait a bit.
 
Thanks guys, I’ve ordered some 5/16 unc they are defo corse threaded head end and unf nut end. The size was the issue but at £3 for 8 it’s worth the risk. Ta all
 
Just measure the studs and they are a mixture of 3/8 and 5/16. The top three holding the inlet are the bigger ones.
 
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