[sdiy] Making holes in plastic

[Fiercefish]

I have a project where I need to make some very neat holes in a plastic enclosure, drilling is not an option due to the size of the holes (about 12mm/ half inch) and I don't have a drill press, also the placement of the holes needs to be very accurate. Which would be a good method?
I was thinking of those devices that go each side of the material and are pulled together by means of tightening a bolt, drawing the two parts together, but I can't remember what they are called nor where I have seen them. Any other suggestions or tips welcomed!

Thanks

FF
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