My local motorfactors do most stud sizes in boxes of 20pcs
For nuts I use k-nut as found them very durable as high carbon steel & locking function works perfect, also they are slim head (reduced hex) so you using smaller spanner/socket which enables easier fitting in tight spots of a manifold, another plus is they available in 1.00 & 1.25 thread pitch in m8 m10 & m12 sizes. the copper nuts are shite on turbo manifolds.
Did use some mechanical self locking (deformed thread) stainless nuts but found they come loose as expand too much with turbo manifold heat.
k-nuts are also reasonable low price so easily refreshed every few years if needed. I bought them in packs of 100 & 50 as worked out far cheaper & soon use them if do a few turbo/manifold jobs.
Another very good option is normal nuts in quality stainless & use locking tab principle from a standard steel-alloy washer.
Principle here is bending short length of washer edge to 90degrees & using air die grinder to cut mating grooves for this washer lip in manifold flange. You then fit manifold and washers so lip in mating grove & fit stainless nuts and bend up aposing edge of washer to lock the nut (ideally need pre-bend washer it a little so easier to do in refined work area).
Quite a lot of faffing around as need do it with thought to access once in fitted position but parts are cheap, they last for almost ever & the stainless nut always comes off without unscrewing the stud.
A lot of professional builds do it that way & a lot of engineers do it on high temp fittings with vibration that need easy dismantling & low corrosion.
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