The Campbell-Napier-Railton Blue Bird from 1931 on a pair of cufflinks.
Interesting to note that Malcolm Campbell, the driver of this and subsequent Blue Bird cars, was knighted in 1931. Not many people can say they achieved such fame from being labelled fast.
Dimensions (LxWxH): 31mm x 10mm x 6mm (approx.)
Weight per cufflink: approx. 7g (light)