Incredibly rare Seth Thomas U. Size 19.5 cm in diameter. A true piece of u.I think it's probably a replacement key. There is some age associated wear to the outer black metal casing and an old repair to the back metal casing only.
The item "Seth Thomas U. S Navy Ships Clock WW2 Rare Collectable Antique" is in sale since Sunday, May 5, 2019. This item is in the category "Antiques\Antique Clocks\Wall Clocks\Post-1900". The seller is "gunners1978" and is located in Worcester, Worcestershire. This item can be shipped worldwide.