How to Determine Pocket Watch Winding-Key Size
"What size winding key fits my vintage pocket watch?"
If you have a key-wind pocket watch and don't have the key to wind it, you'll need to find out what size key you need. To determine what size key is required for winding or setting your vintage pocket watch, you'll need to accurately measure the size of the winding and/or setting square (the square-shaped "shaft" that is either used to wind or set the watch). This measurement must be made accurately, preferably with caliper or micrometer. If you don't know how to find the winding or setting square, you should read our article on how to wind your vintage watch.
Keys (especially modern "reproduction" keys) tend to vary from these precise measurements, so if you think you might need a #5 (for example), you might also want to have a #4 or #6 on hand in case the #5 doesn't quite fit your winding square. Using too large a key will tend to round off the corners on your winding square, and once they are rounded off, you'll no longer be able to wind or set the watch. A key that's too small simply won't fit over the square. The best bet is often to purchase a complete set, as you'll then be able to choose the key(s) that give you the best fit.
Note that key-wind/key-set watches sometimes used the same key for winding and setting, and sometimes used different keys for winding and setting. Be sure to measure both squares if you have a key-wind/key-set watch.
We have full sets of winding keys, similar to those shown below, available on our Watch Accessories page. We also stock single keys in select sizes.
Pocket Watch Winding-Key Size Chart
Most modern keys are marked in Euro sizes
|Size of square (mm)||English Key Size||Euro Key Size (e.g. Bergeon)|