I have a brass key with a hollow circular top which is roughly the shape of a cross. It has a thick tubular middle area with thinner extensions. The bladed section spins 360 degrees on a ratchet / geared mechanism. The blade has the number 6 / a on the bottom and this is repeated on the side of the key. I’ve had it for over thirty years and have never seen anything similar. Can anyone give me an indication re it’s origins. I would have posted a picture but haven’t worked out how to post one yet.