No. 9 in the spare parts picture.
Ø = 13,3mm
Suitable for many different Bing carburetors for example:
Ring float carburetor SRE 10-15mm & SRF 14-17mm
Side float carburetor SSF 15mm / SSH / SSI 9.5-15mm
As well as the more modern carburetor types 15/17/18
Puch / Zündapp / Kreidler / Zweirad Union / Sachs / Ilo m.fl