In the 2006-7 tools catalog, go to page 272. I have never tried
diamond twist drills, but otherwise you can use any of the drills on
the right side of the page of the size you need. I would recommend
that you do not get the value drills, because you’ll use a lot of
them. Sintered is always better. Then on pg. 320, at the bottom,
especially if you’re going to be doing some drilling, get some
tool-cool. Diamond Abrasives: They like all the rpms you can give
them. 50,000 is not too much for a 2mm tool. They must always be
wet, with stone work. And, as with all abrasives, they only cut as
fast as they cut. Be gentle with them, which is to say, firm
pressure. Pushing harder doesn’t cut any faster, it just rips the
diamond off the tool. If you have a high-speed drill press, that
would help. If you need too, or if it’s a shallow hole, you can just
dip the tool frequently, or I used to carve rock crystal in a cool
whip container - flexible sides. Or you can build a dam around the
space out of clay. Then, when you are drilling, since the drill will
load up frequently, you need to pump it - push, pull back, push, pull
back, all the way through. Be aware that drilling a 3mm hole through
1/4" of brazilian agate will probably take 20-30 minutes. It’s not
you, it’s the agate…