Drain plug o-ring for many vintage Honda's. Sometimes gas will appear to be dripping from the drain plug hole, but it might be coming from the float bowl gasket or somewhere else, be sure to find the source of the leak before replacing parts. Not genuine Keihin. These are aftermarket from Taiwan.

Dimensions:

Outer Diameter: 8mm
Inner Diameter: 4.5mm
Thickness: 1.8mm