This is a pack of 10 x copper rivets and washers in '8 gauge' size.
They measure 21mm long in total, with the stem being 19mm long. The base and washer measure 11.5mm across. The width of the stem is 3.9mm.
Copper rivets are fitted by pushing the stem through a hole in your leather, adding the washer and tapping it down flush with your leather. Using end cutters
you then cut off any excess stem length, leaving yourself with approx 3-4mm to hammer down into a dome shape using an 8 guage copper rivet fixing tool.