1979 A1 Pilot Idle adjustment

Is this an air or fuel adjustment? Seem to recall if screw is on Venturi side, it's an air bleed control screw.
If on the cylinder side, it's actually metering fuel?

I want to 'fatten' the mixture on 3 of my cylinders just a tad.

Pics of Plugs

They are fuel enrichers. In for lean, out for richer.