Larry,
The 1922 Buick Sports Roadster radiator cap I am looking for is as follows: Outside Diameter is 2-1/2". Inside Diameter is 2". There are five (5) threads and they appear to be "fine" as opposed to "coarse". The cap is steel with what looks like to be a bakelite edge.
Do you know if a Durant radiator cap would possibly fit?
If you are comfortable to have Howard call you directly so the two of you can talk, please email me your telephone number and I will forward it to him. My email is: pjwc4@att.net.
Also, if you receive texts, I can forward pictures of the outside and inside of the radiator cap he has.
Thank you, PJ