Hello, what effect would a mainspring have that has been changed from the original size, say stronger or less than the original.
Thank you
AL

The main issue seems to be the width which should not jam up between the mainspring Barrel and Barrel Cover but have no more than 0.020" (0.5mm) clearance BELOW the inside face of the barrel cover.

When I change a Mainspring, I always compare and match the width and thickness between the "old" one and the new one I am installing.

There are three basic elements of mainspring "Size", Thickness, Width and Length. These were re-calculated by some sort of early method to derive "Duration" and "Strength". As the modulus of elasticity of the steel used on (good) old mainsprings had to deviate by at least 25%, these calculations were approximate at best.

In fact the real life observations of Mainspring "size" effects are two-fold;

First, when we clean watches that keep time but show signs (shorter balance swing, etc.) a service is due, we often remove a mainspring to find it is almost completely compressed yet it still runs the watch successfully. So much for "Strength", even after cleaning, even this "tired" mainspring can usually power the watch for 30+ hours.

Second, the increased length and greatly reduced thickness of common width mainsprings used on the 60 (and 48) hour Illinois Model 10 and up watches show little or no change in watch performance. So goes the idea of "Strength" as a function of thickness OR length.

David.thank you very much this answered my question