My XC90 got rear ended and we're going to be getting a new bumper. I'm hoping I could take this opporunity to install a generic reverse backup system. Body shop can order the bumper with or without the factory holes. I've found generic systems where most require a 20mm hole, a few require 21mm. I've even seen mention of 22mm sensors.<p>Can anybody tell me what diameter the factory holes are? And is it a nice clean flat hole that one could just snap a sensor into?<p>thanks!