In the picture directly above, you will see a .045" thick brass washer just above the hex shape of the soldered spray bar assembly, next to the aluminum carburetor bottom plate. Why is it there, when it doesn't appear in any of the solid models. Well, my friends, that is the "bit" that buys me some tolerance on all the pieces that screw together and have to meet fairly tight "end gap" tolerances. If the spray bar screws too far into the carburetor bottom plate, then it will press against the underside of the throttle barrel and prevent it from being turned. During final assembly, I did a bit of measuring and determined that a washer that thick would let me tighten everything "snug" and still have a freely rotating throttle barrel. Probably if I built ten more identical carburetors, that washer would end up being a different thickness on every one of them.----Brian