Engine valve yes. Probably ag or industrial. It's been a while sense they made em with the notch in the center. That was for hand lapping. There was a little gadget with a hand crank and a key that fit in the notch. When you cranked it, it reciprocated back and forth. You buttered the valve with an abrasive compound and the result was a valve and seat that made a perfect seal together. Because the head is so thick it was almost certainly a very low RPM engine with a long stroke. Since there is no accumulation of lead oxide on the back of the valve I'd say it's an intake valve which also explains the large diameter. It looks around 2". I'm thinking perhaps a hit and miss engine early 20th century.
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