Hi Brothers - I have an 18s Waltham P.S. Bartlett 17J with a broken mainspring. I would like to know the number(s) of replacement spring for this watch - S/N 8,510,466
I believe it to be an 1883 model. Any info is greatly appreciated.

Sir Clark,

Like to go with part # 2203 on the 1883 model. Should have a "T" - end

Thank you Jon. I have lost my old Swartchild parts book, you are a great help.