I have 40mm Weber IDFs with the air filter bracket for a crossbar linkage.
(I use Tangerine's cable throttle, so I cut the supports off the filter brackets and use them purely for the air filters).

Well these "standard" air filter brackets are designed to fit Weber 44mm so the holes in the top of the plate are larger than the venturis on the carb.
Now when you bolt down the velocity stacks, there is a gap between the velocity stack and the opening of the carb where the vel. stack tapers down to 40mm, then the filter bracket opens up to 44mm, then the carb goes back to 40mm.

When I ordered similar filter brackets many years ago for Dellortos, they came with rubber "rings" that filled in this gap perfectly.

I cannot seem to find these rings, and cannot find anyone on the phone from CBperformance or WeberDirect that knows what the hell I am talking about.

I could easily make some from rubber, or fill the gap with something, but I dont want to take any chances that the material I choose is gas compatible, and cannot degrade and fall in the carb.

So I am about to pay a machinist to make me some Al. rings to my specified dimensions.

Before I do that: Does anyone know what I am talking about and possibly where to find some?!?

Any help is appreciated.

I made my own aluminum rings to fill the gap when I encountered a similar situation on my race car carbs.
I was lucky to have some tubing on hand that only needed a little removal from both ID and OD.
AFAIK there's no off the shelf parts available for that purpose.

So if I dont get any other ideas, it sounds like I found my machinist.
Got any of that pipe left?

I'll measure them today.

Its funny,
I was moving stuff around yesterday looking for something and picked up an old piece of note paper with a circular drawing on it.
If I'm not mistaken, the drawing has the dimensions of the rings I made.
For mine the ID was tapered from 42 to 45 mm, OD was 47.75 mm, height 4.2 mm.
I made those pieces at least 5 years ago, not even sure what carbs they're in now.