SpankedYA!

I use 18-1.5 jam nuts.

-SKUM-

My local hardwere store dosent cary any 18x1.5 Otherwise I would use them. Almost every auto parts store has anti-foulers in the HELP! section.

Toysrme

HF step bit, use cutting oil, they last along time.

-SKUM-

I always throw a bunch of oil on it as I drill with it.

gon3r

i just use a 7/8" drill. as mentioned above, the step drills don't last too long when doing stainless.

HiProfile

I try to use the step bits to make the triagle'd holes round. W/o a drillpress, my drillbits always cut the slightly triangle holes which annoy me. I go closer to 3/4", but 7/8 will work too. Technically 18mm (~0.7") is the outside thread size, so you want to be somewhere around there.

turbob16hatch

i think i use a 1" hole saw from fastenal, and i buy SS o2 bungs from my local muffler wholesaler for like $1/each.

Smith-02

if you use a holesaw, they get hotter than a drillbit will. keep a can of wd40 on that bit, metal holesaws aren't cheap!

Toysrme

Word thatx 5,000, a good metal holesaw may cost $30-40+ a pop!

Guys, buy a metal punch/scribe and tap where you want your hole center so your bit does not wander.
If you are using regular bits, dont take it all in one bit size. Start with a smaller pilot hole and work your way up.
Use recommended RPM if at all possible.
Get you some 3in1 oil to cut with.

Racintweek

we use a 1" endmill. but we also sink the bung in a 1/4 of the way

3/4" will work if you want to surface mount it