I have Elgin size 12 15 jewels grade 315 and need mainspring
can someone give me the right manufacturing #
to order new spring.not sure of the # 1720 or 2239
Thanks.

#1720 to serial #10747000...#2239 began serial #10747001

ok thanks Gary but how did you establish that?
I have this date base from Patrick but still
not being sure on the springs.
Movement S/N 30411014

Information is in the Elgin Genuine Material Catalog...Not sure of the date of the book but it is the old red looseleaf parts book...

According to your serial number your watch takes #2239...If you want me to I will send you one to try out..

Thanks Gary no need I have few project and will
need to buy few mainsprings for different watches so Thanks for the offer but I will have to wait till I get all parts # and them start ordering.