How to fit an armored crystal

How to Replace a Watch Crystal with a Tension Ring in 5 Easy Steps

The most significant advantage of acrylic crystals is that you can easily polish away scratches to make the crystal look like new again. But if the crystal is cracked or chipped, there’s no other solution than to fit a new crystal.

Tension ring crystals are very common, especially in vintage watches. They’re also called armored watch crystals.

With this guide, you’ll learn how to replace a watch crystal with a tension ring.

Click here to learn how to replace a regular acrylic crystal.

The tools you’ll need

  • Watch case cushion
  • Watchmaker’s hammer
  • Soft brush
  • Digital vernier caliper
  • Dust blower
  • Crystal press
  • Cloth or a piece of plastic
  • New crystal

1. Remove the old crystal

Remove the movement with the dial and hands and store it somewhere safe and away from dust.

Use your thumbs to remove the crystal from the inside.

If that doesn’t work because it’s such a tight fit, you can place the watch case with the crystal upside down on a watch case cushion.

Take your watchmaker’s hammer and use it to give a sharp tap on the inside of the crystal. Repeat if you have to.

2. Clean the inside of the bezel

This is the perfect time to clean the inside of the bezel to create the best fit possible for the new crystal.

Over time, dust and dirt build-up between the crystal and the bezel. Use a soft brush and a dust blower to clean it.

Be careful not to damage the dial or the hands.

3. Measure the inside of the bezel

Use the vernier caliper to measure the inside of the watch bezel (make sure not to damage the dial).

Round off the measurement to the nearest even number. With an armored crystal, you don’t add another 0.2 mm.

Let’s say you measure 31.16 mm. This is rounded off to 31.2 mm.

The crystal that you need to use is 31.2.

I always order one size larger as well, just in case. This may come in handy, especially when the initial measurements are between two sizes.

4. Prepare the crystal press

  • Start with selecting the lower die for your crystal press.

Use one of the straight-walled dies and pick the one that is as large as possible without touching the lugs; otherwise, you can bend or break them.

You can also use the universal lower die if you have one.

How to replace an armored watch crystal
Lower die 34 mm, and a universal lower die
  • Next, select the upper die that will be used to fit the new crystal.

Use a die with angled walls. An armored crystal is beveled, so the walls of the die need to follow the contours of the crystal.

Select the die which fits the crystal and touches the beveled edge of the crystal with the angled walls.

A set of dies with angled walls for armored watch crystals

5. Fit the new crystal

  • Use the dust blower to remove all dust from the inside of the crystal and the dial. You don’t want to discover any dust after you’ve successfully fitted a new crystal.
  • Use a piece of plastic or a cloth to cover the lower die and place the watch case on it with the case back down. You could put some plastic or a cloth on the crystal as well, so you don’t scratch it. This is especially useful if your crystal press uses aluminum dies.
  • Bring down the upper die and see if everything is positioned correctly. If so, begin to apply pressure until you feel or hear the crystal click into place. This usually doesn’t take long.
How to replace a watch crystal with a tension ring
Gently press down on the crystal until you feel or hear it click into place
  • Check if the crystal is fitted all the way correctly around.

Finishing touch

Test the new crystal. You should fit one size larger if the crystal is too loose.

If everything checks out…job well done!

Do you have any additional tips? Leave them in the comments below.

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2 thoughts on “How to Replace a Watch Crystal with a Tension Ring in 5 Easy Steps”

  1. A very informative post, thank you! It is definitely something that I will be referring back to when replacing tension ring crystals.

    Would this method also be applicable to the Omega Seamaster De Ville unishell/monocoque case? I have tried this before, pressing the crystal into the bezel – ended in disaster. The crystal completely shattered as the tension ring seemed to be pressing against the front of the bezel, unable to squeeze in.

    The pieces were positioned in this order:
    • Top: crystal with tension ring
    • Middle: bezel
    • Bottom: watch case

    Or should I have arranged it like this below instead?
    • Top: bezel
    • Middle: crystal with tension ring
    • Bottom: watch case

    Thank you for your advice and I look forward to hearing from you soon!

    1. Hi, normally the bezel goes on last. Those unishell cases have some tricky crystals, so you might need to order an original one matching the reference number.

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