This is the threaded piece that holds the Main Jet / Emulsion Tube / Air Jet assembly in place in the Weber DCOE or 48 IDA (dual throat) carburetor. Two used per carburetor (one per emulsion tube assembly). Sold individually.
Not used in the DGV series or IDA Triple. The 40 DCO 3 and IDF series carburetors use a different holder that is not interchangeable.