funny you should ask. i just had 12 valve stems tested at a lab for their r scale hardness. anyway....
the threaded stud is likely in usa terms a B7 or called grade 8. very hard because they've been treated. in metric terms 8.8 is equivilent to our grade 5 tough but not case hardened like B7. from there they go something like 10.2 , 12.2 etc:.
frankly if you cut thru the case hardening you've got untreated steel that won't be that tough. in general carbide cutters treated or with special coatings can machine M2 HHS steel. so in real time cutting this b7 type material is easy.
if you want a hard finished stud i would suggest having a machine shop thread some 1145 grade bar stock then have that heat treated. that way you can work the steel to what you want without changing the integrity of the piece.
if you know someone with a warner swasey turret lathe this would be a piece of cake.
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