This is the threaded piece that holds the Main Jet / Emulsion Tube / Air Jet assembly in place in the Weber DCOE or IDA (dual throat) carburetors. Two used per carburetor (one per emulsion tube assembly). Sold individually.
Not used in the DGV series or IDA Triple. The 40 DCO 3 used a different holder that is not interchangeable. Most IDF series carburetors (including all current production) use the longer WC-52580.006 holder, but some older IDF carbs made for street or OEM applications may have been equipped with this short version from the Weber factory. Either one will fit the IDF, but the longer version will not fit DCOE or IDA.
Note: Fits genuine Weber (made in Italy or made in Spain) carburetors only! Does not fit most copies, Asian knock-offs, or work-alikes.