Air Mag Index Assist Pin Original O-Ring 4.5x1.2 (2.1x1.2mm) (NBR90) for K1. Part Nº 51 of Huben · Spare Parts for K1 · Diagram 2 · Receiver/Main body.
China: External diameter X section => 4.5x1.2
Many other countries: Internal diameter X section => 2,1x1,2mm