Found on the Folly - Interesting Jeppe History - Mysterious object, help me find out what it is?

Interesting object found on the Folly.  It is attracted by a magnet and very rusted.  Measures 10.5 cm x 6 cm.

I am stumped!  It reminds me of a winding key for an old clock.  In this case a gigantic clock ... or the little gadget used to open a sardine tin .......... a giant sized one!!

Any ideas?  Please help me identify the object?

Unidentified Object found on Collard's Folly