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 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 (for example, if a sterling ear post is soldered to the back of a piece of silver clay), the item could then only be marked "sterling silver". The bent stamp has the advantage of fitting inside of a ring shank to mark rings as well as other items.