OH yes, in the second carb> that is the jet for the second carb. You can get those jets for the "E" models 1994 XT600EF Yamaha Motorcycle CARBURETOR Diagram and Parts

They may be a smaller size than your but can be drilled out if needed. I have gotten some of the other jets and carb parts and they fit the older models. It looks like it may work but a couple of the parts might have to be switched over due to some differences in the gas feed tube/hose from the first carb.

Ah. I knew a table of data from a German site I think I found here might come in useful. Been in my favourites for ages...

Have a look at the carburetor main jet left/right row.
Clicky

I think Geschischregulierschraube is pilot screw base position. Ignore this if you don't know for sure if your carb inlet rubbers are reasonably new. Both mine needed another 3 turns out with old but "re-sealed" (actually as leaky as hell) rubbers.