3-1/2" long .999FS quality marking stamp for fine silver. A "quality mark" is the little number or letters that indicate what metal and purity is used in an item made of a precious metal. By law, this stamp can only be used to mark an item that is made purely from .999 fine silver. Do not use this stamp to mark items that have sterling silver permanently attached. For items containing any amount of sterling silver it can only be marked as sterling and not fine silver. If you have a metal clay piece and you solder or fire in place a sterling silver ear post or fire a sterling silver setting in place, that item is no longer pure silver and can't be marked as such. For any fine silver item that you add sterling silver to, you can then only be mark is as "sterling silver"