Sold EACH...... Order 1 to add 1 kit to 1 carb. Order 2 to add 1 kit on each of 2 carbs.
These things are found on BMW R90S carbies for a balance tube to be fitted. They are a press fit item installed opposite the mixture screw. Yes you need to drill a small hole into the carb body for this to work. This procedure is outlines on various BMW forums..... When I find the time I will add the info here.