There's a hole in my ca-arb, dear Liza...

I stripped a Dellorto carb today - MA19BS7 - there seems to be something missing from the hole to the left of the main jet nut - the hole's threaded and as a guide to size, the screw that holds the slide straight fits the hole/threads perfectly.
Any guesses what it is, and should there be something in there?
Any guesses what it is, and should there be something in there?