Thimbles such as those can be found in the same spots old coins are found. I got some myself some are brass, some silver. They also usally have a number on them which is the size number. Some have advertizing on them. Silver ones are harder to find, if dropped they looked for them, they were the prize thimble most likly a gift. The brass read low, so you might want to dig the iffy signals that is where they read at.