Pocket Watch Sizes
A 16 size Hamilton 992B.
These are the standardized diameters of pocket watch movements.
A watch movement is the mechanics that sits inside a watch case.
The outside diameter of these cases (seen in gold in the sample above) will of course be bigger. Case outer diameters are not standardized, while the diameter of the movements that go inside these cases are:
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Pocket Watch Size Formula
Pocket watch sizes are based on 30ths of an inch.
The formula is simple:
Diameter of movement = ((Size + 35) / 30) inches.
For millimeters, multiply inches by 25.4.
For example, for a size 16 watch:
((Size + 35) / 30) inches =
((16+35)/30) inches =
51/30 inches = 1.7 inches.
1.7 inches x 25.4 = 43.18 millimeters.
If size is 0, use 0. If size is 2-0, use -1. If size is 3-0, use -2 etc.
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