As a seller of vintage watch crystals, the most asked question I get is “what is the correct crystal for my wristwatch?”
Sometimes the case manufacture used a 3-6 digit code stamped or printed on the inside of the case back to identify the correct replacement, Sometimes a clear close-up photo of the bezel of the watch is all that is needed if it is a popular named collectible, but with the many different brands and models that were produced over the years, the result is over 10,000 different shaped & sized crystals and finding the correct one is not always as simple as taking a photo of the watch.
If you don’t have a case number, and are not sure if your watch had a name, the first thing you will need to do is measure the old crystal with a digital calipers. It is best to remove it from the bezel, clean the old crystal glue residue away and measure the length & width at the greatest points in millimeters, write those measurements down and then measure the crystal grooves on the bezel the same way (make sure those are also free of any crystal glue residue) and average the two measurements.
The next step is to determine the shape of the crystal.
The last step is to determine if the crystal and bezel has any curvature to one or both measurements or if it is completely flat. To do this just lay the old crystal on a flat surface and check both measurements and confirm them with the curvature of the bezel. The curvature can be slight or quite pronounced, so check it closely. The broken lines on the photo below represents the curvature of the edge of the crystal and matching grooves on the bezel.
Now that you have gathered all of this information, lets put it to use! On the Bulova example above, the digital caliper & crystal groove measurement averaged out to 23.0 x 23.0 mm, the crystal is cushion or convex shaped and is also curved about the same on both measurements. A quick look at the crystal books and behold, we have a CMY305-2E listed as fitting a Bulova Ranger!
Now just because the packet and crystal book list this as fitting a Bulova Ranger does not necessarily indicate the correct name of the watch, many crystals will fit other models as well as brands of watches. The important thing is the measurements, shape, and curvature of the crystal.
The majority of the crystals I carry are the GS (Germanow-Simon Machine Co.) brand which are Acrylic in composition. I occasionally have other manufacturers like Electro Seal and SUC on hand as well as the some of the glass crystal brands like Watchcraft, B.B. and Federal. I recommend the acrylic style because they are cheaper, easier to fit, and if you have ever broken a glass crystal on a watch, the tiny glass fragments will get into the movement and cause all kinds of grief and extra expense to have it serviced.
A quick explanation of the GS parts numbers are as follows;
C = Cylinder style (raised sides to make it look like very thick glass)
M = Military style (curvature to one or both dimensions)
Y = Convex shape
305-2E = Part number
If the watch bezel and crystal are flat, the part number would leave out the “M” and only have one or two letters before the part number. (Example X994 or CS445)
GS also makes a alternate crystal for this watch which is thinner, and more like what probably came from the factory, the part number is PMY305-2E. The P stands for P quality. The picture below is showing the difference between the two styles for a Hamilton Perry.
Most all replacement crystals require some final fitting before they are glued in, a flexible emery board used to file your fingernails works perfect for this step. Never try forcing the crystal into the groove on the bezel, you will end up with a cracked crystal, it should snap into place with very little effort. If it doesn’t, use your emery board to file the edges a little at a time until it fits.
This guide should help you with the basics on finding the right crystal for your vintage watch, while it is using shaped watches as a example, round crystals are measured the same way but also require a height measurement so the hands have ample room to move. Removal/installation may require special tools like a crystal lift or press to get the job done. Water resistant watches will require new case gaskets and a waterproof test to make sure it is sealed to specs. If you are not comfortable opening a watch up to remove, measure, and install a new crystal, seek out a professional like a Jeweler or Watchmaker to do it for you.
Thank you for checking out this guide on selecting the proper crystal, I hope to soon have another guide on the proper fitting/installation of your new crystal and some tips on restoring your vintage watches.