Key cufflinks - there are corny lines here about unlocking someone's heart or the key to the door. This would be a great way to carry the keys to your luggage when flying, but unlikely to work, sorry!
Dimensions (LxWxH): 23mm x 12mm x 5mm (approx.)
Weight per cufflink: approx. 3g (light)
Size = x mm (W x H)