Purpose of this GUIDE:
To learn how to measure basic watch crystals that are round. The article will cover the difference between standard low dome plastic crystals, standard high dome plastic crystals and flat mineral glass crystals. This article does not cover fancy shaped crystals at all. Fancy shaped crystals are defined as anything other than a standard round.
Many companies sell watch crystals on EBAY. There is a need to have basic knowledge on HOW TO FIT A CRYSTAL and it is not rocket science. The basic explanation is that you need to fill the HOLE in the top of the watch with the proper crystal.
- Openface Pocket Watches require LOW DOME CRYSTALS.
- Pocket Watches with LIDS are called a HUNTING CASE or HUNTERS CASE pocket watch. They require crystals that are called SAVONETTES or GHC or HC crystals.
- Most wristwatches that require a plastic crystal can be fitted with a PHD, also called a HIGH DOME.
- Many modern watches that require a flat glass crystal, use a MINERAL GLASS crystal that is flat. These will usually fit into a PLASTIC GASKET.
- Rolex Watches that have a BEZEL inserted over the crystal are not part of this article. Furthermore, Rolex Crystals need to be fitted by Case NUMBER. This number can be found, between the lugs at the 12 o'clock position. Then, this can be ordered from that number.
- Omega Watches that are fitted for crystals require their case number which is located on the inside of the case back. Omega crystals cannot be ordered from a style or with measurements. The case number is manditory.
- Seiko, Pulsar, Lorus can be ordered from their case number. If the watch takes a standard ROUND FLAT crystal and has no rotating bezel, most of the time it can be fitted with a general MINERAL GLASS flat crystal also called an MG. Seiko case numbers are in the following format: xxxx-xxxx. These can be alpha and numeric as well as needing the '-' in between the two sets of numbers.
- Citizen Crystals are designated by a case number. Usually, one or four digits, then a hyphen followed by the remainder, such as 4-60394 or 6031-412598.
- Many others have to be ordered directly from the manufacturer.
There are crystals made of PLASTIC, GLASS and SAPPHIRE materials available for watches. Depending upon the brand and style of watch, that will determine what kind of crystal is necessary.
- Most all pocket watches today are fitted with PLASTIC CRYSTALS as described above. When these were originally made, glass was used. During the period 1940 and on, PLASTIC has been substituted for many reasons, such as less chance of breakage.
- Most Wristwatches that have a domed crystal and use a PHD. These are made of a variety of plastics and offer the ability to resist breakage. Watches that have a high dome plastic crystal with a metal ring are tension ring crystals. They require a special tool to install.
- Mineral Glass crystals are flat and made of a hardened glass.
- Sapphire crystals are made of synthetic sapphire material.
There are three pictures above. This bezel is from a POCKET WATCH, OPENFACED style. In the picture on the LEFT side, you can see the ridge in which we need to measure for the crystal. We use a digital caliper as shown in the MIDDLE picture placed in the recess of the ridge. The caliper is placed across the center of the bezel of the watch. Accurate measurement is needed to get the crystal to be fitted correctly. Whether the watch is a pocket watch or wristwatch, the basic procedure is the same. The picture on the far RIGHT shows the caliper centered on the watch bezel.
The picture above on the LEFT shows the PK and PHD crystal. In the middle picture is the PK crystal in a caliper. Notice how it measures about 2.7 MM thick. THe PHD on the far RIGHT measures 3.91 mm thick. The PK is referred to as a LOW DOME crystal. The PHD is referred to as a HIGH DOME. There is also an XHD crystal that is called an EXTRA HIGH DOME. These XHD crystals are rarely used.
Depending upon how the crystal is going to be installed either with a CRYSTAL LIFT or glued in will depend upon what size you will need to order. Typically, glued in will require the crystal to be the same size as the measurement or a tenth of a millimeter smaller. For example, for glued in crystal, if the bezel measures 22.2, you would need this size or 22.1 or 22.0. If you are going to fit with a CRYSTAL LIFT, the crystal will need to be the next size up or in this example 22.3 so it will be 1/10th larger.
On the LEFT above, is the TWO ET Crystals. ET stands for EVER-TIGHT and uses a RING as displayed in the picture in the CENTER above. These come in two different colors, YELLOW and WHITE (some people refer to this a silver). The height of the crystal is the same as a PHD. These are commonly found in Waterproof watches made from many vendors. If these were to be fitted by the consumer, a special press is required for insertion. The press PRESSURES the crystal into the bezel. COMMON RULE OF THUMB with the crystal is that if the bezel measures 30.0, then a 30.1mm would be ordered to allow for a snap fit. In most cases, this should be done by a watchmaking professional.
Mineral Glass Crystals or MG crystals are measured the same as PHD or PK crystals. However, unlike the PHD or PK, there is the issue also of the thickness of the glass. Mineral Glass crystals are sold in thicknesses of 1.00 mm, 1.5 mm, 2.0 mm, 2.5 mm and 3.0 mm. Mineral Glass crystals are hardened glass. This is accomplished by taking the plate glass and putting it in an oven to temper or harden it. MG crystals need to be exactly the size or 1/10th of a millimeter less. These are usually glued into place using either UV (Ultra Violet Cement) or 2 part Jewelers Epoxy. Sometimes these are fitted into a plastic gasket. The gasket is a pressure fit and needs to be pressed into place with either a flat even press on a flat surface or using a Watchmakers Press.
Fitting the crystal into a gasket can be a difficult ordeal. As these gaskets are often dimpled or suffer cracking over years of service. In most cases these can be removed and the crystal fitted to the watch without use of this gasket.
In conclusion, this is a brief outline of a simple process that becomes easier with practice.