That's if you're buying small quantities on ebay. If you were buying sackfuls for a furniture factory, it would be BZP, cheap Chinese steel made without nickel.
The button-headed hex-socket stainless screw, M6, 20mm or so, is often bought, a dozen or so at a time, by porky old bikers with money to spaff up the wall. There are plenty of vendors willing to take it.
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