These idle jets are located just below the top plate on either side of the float bowl on the Weber DCN(F) and IDF carburetors. Two jets are required per carburetor. Note the unusual "necked-down" portion near the air inlet hole on the side of the jet. Most other Weber models use idle jets with a consistent OD at the side hole location. Sold individually.
Larger size numbers indicate a richer idle mixture. Most applications work well with a 45 or 50 size, but many Maserati applications were originally fitted with the 60 size. The air inlet hole on the side is not calibrated, so there are no "F" numbers on these jets. Idle air metering is determined by the hole in the jet holder.