Next time try TapMagic instead of the green goopy stuff, and 303 stainless is a free machining grade that takes a lot of frustration away from working stainless; I used it extensively in my product line of winemaking tools in place of 304 with never a problem.Tap broke off right at the last thread. The other half is just a straight shank.
I don't remember the grade... It was blue and red.... Lol
The lube was the green goopy stuff.
I drilled the hole 17/32" so, slightly oversized for a 5/16-18.