Little filters in the carbs?

[deltarider]

It's at least 35 years ago that I opened my carbs out of curiosity. Now I seem to remember that, after I had removed the brass valve seats, that in the holes where they sit, there was... what was it? Was it a little very fine gauze filter, was it some felt or was it just accumulated dust? It's not in the exploded view. 

[Arch stanton]

I don't know about 550,s but 750F1,s certainly have them.

[Bryanj]

Its something thar is either part of the needle body or pressed into the carb body, either way not available seperately