In the days before roads had tarmac surfaces, pattens such as these were fastened beneath the wooden soles of clogs, thus enabling the wearer to get around in muddy conditions reasonably well. They were widely used, but are uncommon detecting finds. For one thing, most detectorists I know avoid signals that indicate iron objects, as they are most likely to be modern junk. Also, iron corrodes. After a couple of hundred years in the ground, there might not be much left to find.