2.5" Center Inlet, 2.5" Offset Outlet.
I mounted the hella's on some 1 3/4" x 3/16" flat-stock steel. Had to put a little offset and a twist in them, and then used 1/2" hardware (bolt, lock/fender/square washers) to secure it.
As for the tip it has just enough clearance all the way around, maybe 1/8". It's big enouhg diameter and far enough back in the system to not get super hot and melt the bumper/bubble the paint. I would have trimmed more out but I already had enough urethane shavings all over me for one day.
