Custom Bowl - Designed to eliminate the need and expense of a spacer spool and decrease rig up time. Custom bowls are used when the height between the blowout preventer stack and the bowl outlet flange is greater than that of a standard nipple-up bowl. Custom bowls can be built to exact rig height specifications and have flange configurations to match BOP stacks from 7 1/16" 3000 to 30" 1000.