I don't know if you want to include Dayton branded bikes, but I think it may be of interest for some folks. To the best of my knowledge, mine is a 1918 model 172 "Motorbike". It appears to be the same as appears in images of a 1920 catalogue on Nostalgic.net (Thanks Dave). Mine has a serial number "721242". I don't know if there is any rhyme or reason to their serial numbers. I worked at a company building frames for recumbent bikes in the 1990s, & the serial number coding was ridiculous. Each year, the numbers simply started over at "0001"! I suggested we have a year (& possibly a model code), but my suggestion was summarily dismissed... They went bankrupt...