Old Style window lock key

These old style keys work on the principle of a female eccentric circle.

The lock has the male part and the key the female part.

These keys were used on locks that are quite antiquated now and
if they haven’t been used for a long time are likely to be stuck, stiff
or painted shut. If the lock will not rotate with the key it is possible
that the key will lose its eccentricity and ‘round over’ rendering it
useless, so buyer beware there is no guarantee on these old legacy products.