I'm not sure about the metal wheels, but I know the mid-seventies plastic wheels were manufactured by another company for Weber. I would imagine Weber would have taken the same approach earlier as well.
The attached picture is a wheel off of a 1975 kettle. The back says "Circle Eng. Co." "Chicago ILL" "Pat No. [illedgible]". I've been looking for NOS wheels of this generation but never had any luck.
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