when you actually see a tire groover then it will make sense. but the blades are just V shaped and are clamped to the tip of the groove iron. which you plug into any regualr home outlet and it heats the tip and thus the blade. since the blade is V shaped the deeper you go the wider the groove, but at its widest its only about 3/8 or so. you can adjust the blade on the tip too to go deeper in the lugs. but i wouldnt get too close to the actual carcass of the tire. when i did mine i left about the thickness of the wear bars. so maybe 1/32 remaining on the carcass.
on a side note, the iron can be plugged into a household socket... but dont groove on your living room. its burnt rubber so it smells a little, and it leaves a bunch of rubber slivers all over the place.
pm if you guys want to borrow it. like i said, about half hour for a 33" tire. and i used about 1 blade for 2 tires.
pm me if you're interested or have questions:)