Take-off/used large painted aluminum fuel cap with gasket and retainer chain.  The top measures about 4" across and the opening is about 3.5".  It has 3 large threads to screw onto the tank neck.  There is a spring loaded breather built in.  The cap comes with retainer chain and gasket.  The brand name, model, and fitment are unknown.
Shipping to the lower 48 USA states only.