NavList:

It comes from somewhere dirty, so it’s probably engineering.  The rivets look like copper, so it’s probably metal even though it looks as if it could be any material.  The centre hole, the rivet in the link rod and the top (in the photo) edge of the radius arm are all in line.  Also, the top edge of the radius arm appears to have a rest position exactly on the centre line of the middle spoke, so it’s meant to be set up precisely, possibly using the ring on the radius arm.  This is possibly an eccentric, or possibly just end-stops, or more likely you can move the link arm in and out along the radius arm to increase or decrease the amount of travel of the link arm for a given movement of the radius arm.
This might be the control lever end of a piece of machinery, possibly for Stephenson’s or Walschaert’s valve gear for a steam engine.  In line with the central spoke is neutral.   Forward or back is forward or reverse, the amount is the speed/gear; a little to start, more as the machine speeds up.  Could that be what the lettering on the rim once said?   Elementary my dear Watson, or should it be Euclid?  DaveP