Calculate the Thickness of an In-Barrel Mainspring

A properly sized mainspring will fill half of the available area in the barrel. It is easy to calculate the dimensions of the barrel.

Calculator: Mainspring Thickness
Barrel Measurements
Inside Diameter of the Barrel
Diameter of the Barrel Arbor
Mainspring Length
Results
Needed Mainspring Thickness:

Formula

TMS = 1 x ( ( x DB2 ) - ( x DA2 ) )
2LMS
4 4

where,
  • TMS is the mainspring thickness
  • LMS is the mainspring length
  • DB is the inside diameter of the barrel
  • DA is the outside diameter of the barrel arbor

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