I’ve been fielding a few questions about the actual dimensions. I’ll try and get a good graphic from my OEM, but for now: I use a 7 3/8″ hole. It could be a little smaller, but this gives you some room for error. The OD is 8.25″ and the fastener centers are 7 7/8″ across. For those of you flush mounting, the basket/gasket edge is 5/16″ (don’t forget room for your gasket!). BTW, my BIB’s have bolts just a little under 8 3/8″ across. I put a little dent in the outside of the basket for each bolt, and secure my BetsyK’s from outside the frame under the edge of button head cap screws. I works really slick, because I can swap drivers (well, those I’ve dented) by removing only two screws and loosening the bottom two. pj