Large Silver Needle The purpose of the silver needle has been widely debated. It was thought to be a surgeon’s needle or even a sail needle for repairing the ship’s sails. However, its large size makes it unlikely for medical use, and the softness of silver makes it difficult to use on sailcloth. One possibility is that it is a sacking needle, used to sew sacks of gunpowder closed. Being nonferrous, it would not have caused a spark when used near such a volatile substance.