I just found this patent from Sept. 4, 1917 that my Great Grandfather designed and filed for patent in 1916. How would I find out if it was bought, used, etc.?
Congratulations on discovering your Great Grandfather's patent. Unfortunately I don't know of any special way of finding out if it was licensed, used, etc. beyond normal web searching techniques. The patent probably expired around 1934 so there is no financial value to it at this point. By the way, it is a full fledged utility patent, not a design patent.