where to get glass bit?

[Rikko]

You can get an almost perfectly round hole with a Dremel if you mark the hole cleanly. I always mark up the whole area with a Jiffy marker and then scratch out a circle with a compass.. You can really see where the ink has been scraped away and just Dremel it away. I find you get a much smaller hole than you might otherwise get anyways - but maybe you can find a more precise holesaw. When I took an exact measurement of the bulkhead I used with calipers it was a good 1/4" (diameter) smaller than a "standard" size.