I would like to know the model number and any other info. Also need the mainspring part number. Serial number is 3406252 and is on a 21 jewel 16s Burlington.

Hi Richard,
I believe you have a 21j, model 9, open face, lever set, grade 107, year 1918. There are a number of different mainsprings for the 16s Illinois. Your best bet is to measure the spring, including the length.

Thank you Brian. The length is 22 1/2 and there are two springs of that length. One has a T end and the one I have has the tabs about 1/4 inch from the mainspring end. I don't know what they call this type of end. I think the spring I need is 47331. This spring fits the model 9 and those with the motor barrel.

Richard-

A model 9 should take one of the three following springs: 47320, 47321, 47322. The difference is the strength (thickness) of the springs. The 47320 is .17mm thick, 47321 is .18mm thick, and 47322 is .185mm thick.

Jared

Thanks Jared. There are some 47331 mainsprings for sale on this forum. The only difference I can see, being it is .175mm thick. Would this work?