5/16-18 x 1" Header Bolts Do They Exist?

No way to use 12 point on four of the bolts, not enough room to get a wrench on them (TTI Headers). Found what I needed at Jegs but it was a direct ship from Hedmen and took 4 days. I should say they will work but I would like to have had stainless steel.

Looked up counterbore screws/bolts with no luck in 6 point zinc or stainless. I didn't spend much time searching as I already had the Hedman bolts.