This may seem like a silly question for many of you but here goes. I recently bought a bunch of mainsprings most of which are Marco brand. All of the packets are marked with part number and brand/size watch they fit. Some of the packets are marked "for overbanking watches". How are these different than regular mainsprings, and are they suitable for a watch that is not overbanking. Are these common or is this somewhat of an oddity?

Mike,
I think they are referring to a watch that is running too strong and is knocking, you may well find if you measure them against a same type, they will be slightly thinner and therefore less powerful and help in reducing the amplitude a selection of spring in sizes is always nice to have and can help fine tune a watch..

Thanks Chris. That was what I figured but wasn't sure.