Barrel Arbor
The barrel axis, around which the mainspring coils. M. Rose calls attention to the importance of the proper diameter of barrel arbors, and points out that if the arbor is too large part of the elastic reaction of the spring will be wasted, and if too small there will be a rupture or straining of the spring and therefore a loss of elastic reaction. It is, then, he says, the thickness of spring that determines the diameter of the arbor or conversely, and from this it follows that the diameter is not an arbitrary quantity, since it depends on the duration of flexible and thickness of spring. See Mainsprings.