Now, there is the usual way...bench grinder to remove the taper tip.
Or there's the Lewis Dumb way - trying to thread hard stainless with a $40 tap.
Snap.
Instant $40 bottoming tap. Ruined $9 stainless bracket (I am NOT going to try to turn the piece out, or alum it out)
And a multitude of cursing.
Lesson learned - more oil, back off to clear chips more often, and stainless is a royal PITA
Ah well, i'll grind it flat now (but it's probably metallurgically effed now, except maybe in aluminium)