O.S. 22781800 Small Carburetor O-Ring #2K/#2SB OSMG7392

Fits: 

O.S. Engines .21 B2101 Speed

O.S. Engines .21 VZ-B V-Spec

O.S. Engines .21 XZ-B

O.S. Engines .21 XZ-B Speed

O.S. Engines .21 XZ-B Speed II