Hello,

in searching for a conversion table for Dennison mainspring dimensions to European standards i found this Elgin most complete database which i post for your perusal

ps pls be aware that the conversion formula
W-Dennison v/s Metric at the end of the page is not correct,
the rest is...
rgds

http://elginwatches.org/databases/mainspring_info.html

Thanks for pointing this out. Always useful.