To use a hole saw in a car roof, Home Depot type or one made for NMO, you simply peel back a little rubber weather seal around the headliner near a door, cut the hole, install the mount and pull the coax towards you and tuck the coax under molding to the floor and to the radio. A professional radio installer NEVER drops the headliner and rarely completely removes molding to route coax.
The whole process takes maybe 5min including sliding a thin sheet of plastic between the headliner and metal roof on some headliners so you don't snag the headliner. That's 5min for the topside work to get the mount and coax in and maybe 15min total for the antenna install including putting on a connector unless its a particularly difficult vehicle. When I was in the business a long time ago a busy day would be 6 or 7 radio and antenna installs per day.
To use a Greenlee punch you have to do at least the same prep, drill a 1/4" hole, then try and get half the punch between the headliner and roof, which is not easy on many vehicles. If you are in the install business you will be out of business soon wasting time putting antenna mounts in using a Greenlee punch.
I'm not saying a Greenlee punch doesn't make a nice hole or it can't be used, its just not the right tool for the radio installer. Any other actual radio installers want to comment?
Some of the comments remind me of a guy I worked with years ago that did things that I thought were silly. For example, we needed a new office light switch installed in a sheetrock wall where an outlet box was needed and wire run to the switch. Most people would use a coarse sheetrock hand saw and cut the hole out in less than a minute with no problems, no pilot hole needed and little mess.
Instead, my work mate liked to use a dremel moto tool with cutoff wheel for some reason and he picked that tool every time we had to cut a hole in sheetrock. It was very slow, very loud and filled the room with fine white dust, plus it prematurely wore out the Dremel with all the fine grit that got sucked through it. Some people use the right tool for the job and others have made up their minds on something else.
prcguy
I've used Greenlee hole punches MANY times and never had a problem with sheet metal car roofs. We always had small square blank metal with the 3/8 hole for the stud and it would punch the sheet metal without the draw bend occurring.
Albeit, the hole punch works better with heavier gauge metal, but car roof's sheet metal can be done if you use the square, ( or round ) blanks to act as a thicker gauge.