Apparently what you want to put into a "railroad watch" is a Mi-Chevee style crystal with a bevel.
They tell me that a glass crystal will snap into the bezel and stay there without any use of glue -- if it is the correct size! Crystals come in sizes that more or less step by 0.1 mm - so if you have a bunch on hand of all possible sizes you can find one that just fits into the hole, then get the next size bigger and snap it in! I have given this the old college try and given up on it. Heating the bezel is how pros do it, but you need a bezel heater with a flat top the bezel can sit on while you snap the crystal in. There is concern about crystals breaking due to thermal shock when doing this, but one fellow reports he sees maybe 2 out of 100 break. In any event, there is no shame in not doing this and finding a crystal that fits nicely (or making one fit nicely) and then using UV curing epoxy to glue it in -- see below.
Also note that cases and watch movements are manufactured independently and are put together later. This means that two identical movements may be in different cases which require different size crystals. So, you have to measure the opening in the bezel of your case.
The pocket watches I have examined have crystals that are either 1.0 or 1.15 mm thick (crystals are available in a variety of thicknesses, including 2.0 mm and even thicker).
Sources for crystals are as follows:
Consider these remarks by "Genway" on the nawcc forums:
Either for glass or plastic crystal, GS cement is not good enough for long term.I said this because I use it for 10 years before I gave it up. GS cement is just too easy to peel off from metal surface, which make it unsuitable for any watch case made out of metal (99%?).
We warranty on all our crystal installation for one year, so this end up 15% crystal is fall off or gone within a year, we not only have to order another crystal for free and spent another labor for doing it better! So my hard learned lesson (cost me thousands before I gave up!) is do not use GS hypo cement for watch crystal!
I use 5 minute Epoxy instead. use tooth pick apply the glue, and even after the glue is settled, within 20 minutes, you can clean it easily with water, once set in one hour, you can not remove it easy. It stay tight as the back case fit to case!
To do a clean work, apply the glue to grove, extra is okay, wipe out within 3 minutes the extra one, only the one in the grove will not be wipe out, so a minimun is left, press the crystal in, wait 10 minutes, use toothpick remove the extra one, at this moment, water will help easy the job, you can even tooth brush it with soup and water, come out clean after dry.
The last 15 years I only use Epoxy for crystal.
See this thread on the nawcc forums.
William White (of White's crystals) posted the following on the ihc185 forums. He makes a strong case for gluing rather than snapping the crystals in via heating the bezel (something I struggled with and gave up on).
If you have a crystal that is already a close fit then cement can be used to secure it, in fact, I would recommend cementing anything that is going to see use as a carry timepiece, no matter how snug the fit is, it can still pop out. For this job I use a clear 2 part epoxy. U.V. cured cement that is made for this purpose is also very strong but the advantage of using epoxy is that it can be softened and removed via boiling in water. Super glue should be avoided as it dries brittle and can leave a foggy mess on adjacent surfaces. The way I cement a crystal in place is to apply several drops around the bezel opening with a small dip oiler, put the crystal in place then turn it slowly (if it's not too tight) to spread the cement evenly. Heating the bezel is a great way to fit a glass tightly and although I don't use this method it has been used for many years and will eliminate the need for any cement... if done properly. The crystal can have no edge damage or rough areas as they will certainly develop into much larger damage once the bezel cools and contracts to its original dimension. Enormous pressure can occur here and transversely, the bezel must also be free of any dents, damage or debris where the crystal seats.
See this thread on the ihc185 forums (entitled "How do you mount watch crystals?").
Tom's notes / tom@mmto.org