I did all my hole saw cuts for my sight glasses with this crappy little kit from the big green shed:
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Used some wd40 to keep everything happy. Hole saws are still fine but I fucked my $20 xu1 drill (it was about 13 years old and I'd built my boat with it so it'd had a good life). Anyway the kit had a hole saw that wasn't too far off the size needed to fit inside the sight glass tee and then I filed/dremelled off the rest with a cheapo cut off wheel on my rotary tool.
Reckon that'd be heaps faster than using a 1" step drill bit and filing. And costs bugger all.
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