minimum 1/8th step up last I checked. I don't like dremel tools for things like this, maybe if you have a really thin hull to work with, and an aggressive carbide bit. Otherwise neater and much faster with the right tool for the job imo. As faster points out, no good if you have to move the hole, but otherwise handy.
They are pretty common, Lee valley charges 9$, but I've seen them all over once I knew the name for them.
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