Changing pocket watch crystal is a pretty straight forward and easy job to do. However, the difficult part is fitting the right crystal to your watch. Unless you have various crystals of different sizes, it is very easy to purchase the wrong size for the first time. That is why watchmakers charge more than the actual crystal cost. Besides the labor, they also need to invest on those watch crystal inventories.

Before you even start looking for the right crystal, you need to measure the size of your watch bezel. First, you need to know the size of your watch bezel opening, which is the distance B (black) indicated in the diagram. If the crystal is too big, it will not be able to pass through the bezel opening. It is also useful to know the size of your crystal seat opening, which is the distance A (red) indicated in the diagram. Make sure the crystal you choose is larger than A. Although you can still glue it onto the bezel if the crystal is smaller than A, the gap between the bezel opening edge and the crystal will be too wide and become noticeable. Ideally, you would choose a crystal size that is slightly larger than the bezel opening (illustrated as distance C (blue) in the diagram), and you can use a hairdryer to heat up the bezel to widen the bezel opening temporally for installation.

The following chart is useful for converting between Ligne and metric crystal sizes.

After knowing the diameter of the crystal, you should also make sure the height of the crystal suits your watch type. Usually, hunter pocket watch crystals are flatter than open-face ones. If you buy an open-face pocket watch crystal for your hunter pocket watch, the tall crystal may prevent you from closing the lid. If you buy a hunter pocket watch crystal for your open-face pocket watch, the flat crystal may prevent the watch hands from moving because the crystal actually touches the watch hand (the part D of the diagram). Usually the seller will indicate the type of crystal he is selling. However, you will never know if it fits your watch until you actually try it. As you can see, the size difference can be as tiny as 0.1mm.

Another thing you need to consider is the material of crystal. Glass offers more clarity and scratch resistance, but it is more fragile than plastic ones. If you have a hunter pocket watch, you can consider a glass crystal because it will be protected by the lid. If you have an open-face pocket watch, plastic might be a better choice if you wear your watch often. Even if you do not drop the watch, glass crystal will still crack if you press on the surface hard enough (e.g. accidentally sitting on the watch).

Now, let's see how pocket watch crystal replacement is done.

First, measure the diameter of the watch bezel opening.

In this case, the diameter is about 44.31mm. From the previous chart, we know that a 44.3mm crystal will definitely be able to pass through the bezel opening. However, for the best fit, we choose a slightly larger one: 44.4mm (19 10/16) crystal.

Here, we use UV glue. Although UV glue is not as strong as other types of glues (e.g. rocket glue), it is clear, easy to clean and allows you infinite amount of time to work with. We will use syringe needle tip to apply the glue.

Before installation, we need to clean the watch bezel. Depends on the type of glue used previously, you can choose different types of cleaner. Here, we just use alcohol. If the bezel cannot be removed from the watch, make sure you use a piece of paper to cover the watch dial for protection. Use the syringe tip to remove any remaining glue residue.

If the crystal you choose is slightly larger than the bezel opening, you will need to use a hairdryer to heat up the watch bezel first. While the bezel is hot, the crystal should be able to fit into the bezel and sit on the crystal seat opening. If the crystal can fit onto the crystal seat directly, you can just start applying UV glue along the crystal edge using the syringe needle tip. Use cotton swabs to remove any excess glue.

Once you are satisfy with the result, you can put the watch under direct sunlight and wait for the UV glue to cure. The process usually takes about 10 to 15 minutes but will be longer if it is cloudy.

Now, you can enjoy the watch with a new crystal after the UV glue is cured. Please note that the crystal edge should be free from any glue residue.
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