Helmet with a roundel image. I imagine these are for an Evel Knievel-type bike rider - but they make me think of USA Gridiron players without the face shield.
Large and heavy cufflinks - be warned!
Dimensions (LxWxH): 18mm x 17mm x 17mm (approx.)
Weight per cufflink: approx. 14.43g (heavy)
Size = x mm (W x H)