Re: how to cut a perfect 4 5/8 hole for a gauge?
 

I use duct tape, several layers to protect the dash. 4.5" hole saw and then use a drum sander in the cordless drill. They come in all sizes up to a couple of inches and different grits. Rough for cuting to size and fine to smooth out the hole and chamfer it.

But BE CAREFUL!! One slip and well that's what the duct tape is for..

Good luck!