Whether your watch crown is broken or you simply want to exchange it for a larger one that is easier to turn, before you can replace it you will need to measure the size of the crown. Use this guide to learn how to measure a waterproof watch crown.
You can tell that your watch crown is a waterproof one by checking on the watch case for a stamp of “water resistant” or “waterproof”. Watches without this marking will not have a waterproof crown.
The first thing you will need to do is remove the old watch crown. For assistance check out this article on how to remove your watch crown.
Once the old waterproof crown is free of the watch case, lay it out in front of you on your work bench. You will start by taking your digital gauge and using it to measure the outside diameter of the old crown. Open the jaws of the digital gauge wider than the size of the crown and position the jaws on either side of crown. Then close the jaws until they rest snugly against the edges of the crown.
Record the measurement. This will give you the size of the crown you will need to order.
Next you will need to find out what the post size of your crown is. You can do this in a couple different ways either by measuring the case tube sticking out of your waterproof watch or by measuring the crown itself.
If the case tube is still sticking out of the watch case, the easiest way to find the correct post size is to measure the outside diameter of the case tube with your digital gauge. Simply close the jaws around the case tube and record the measurement.
If the case tube is missing, or if you prefer to use a different tool, you can use the optional watch crown gauge and fit the existing watch crown to the post sizes. Simply screw the crown onto the gauge until you find the post the fits the crown perfectly.
You can also measure the crown itself using your digital gauge. Simply turn the crown upside down and use the backward opening jaws to measure the hole in the crown where the post would usually sit. Be sure to repeat this measurement a few times, as it can be difficult to measure such small spaces accurately.
Record the post size measurement on your notepad.
The last measurement you will need will be to find the tap size of the crown. To do this, you will need to remove the watch stem from the watch case and movement. For help doing this, please check out these links:
Be sure to keep the case tube in place while you remove the stem.
Once you have removed the stem of the watch, take your digital gauge and use it to measure the outside diameter at the threaded end portion of the stem. Again, close the jaws around the end of the watch stem until they grip the metal closely.
If the stem has been damaged and you cannot measure the threaded portion, you can use the movement number on the movement itself to look up the correct size stem and tap for the watch.
Record the measurement of the tap size. Sometimes the tap size is not always listed in millimeters, to convert your millimeter measurement to the correct tap size, check out this conversion chart.
Once you have all three measurements in hand you are ready to order your new watch crown. All you have left to do is decide if you want a white or yellow crown to match your watch case and the crown style (flat, dome, jeweled, etc.).