These are a delightful example of easy to wear, light weight carbon and porcelain ball bearing studs.  The posts and backs are in stainless steel.  Interestingly, one may think that ball bearings are cheap, but the bearing ring used in the gearbox is in excess of £1000!  A great gift idea, nice and discreet and unique.
Measurements are:
8mm ball bearing
Stainless Posts 1.3 cm
This will be packed in a black box with a matching black, satin ribbon.