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I was looking at my SAR today, and reazlied that I dont know how it is held in place. Its got to be pretty strong to be able to withstand 300m AND not let water in.

I have read that rolex and UTS use screw in crystals (which I suppose is the preferred method for securing a crystal), but I cant seem to figure out how the crystal is fitted. Im guessing its pressure fitted?
 

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There are several way to fit a crystal. Remember, the water pressure is on the outside trying to force the crystal further into the case.

1) Friction fit, by far the most popular method. If the crystal is glass (mineral or sapphire), there is a nylon gasket placed in the case and the crystal is forced into the gasket. The gasket expands into the case (which usually has an under cut to lock the gasket in place) and friction between the gasket and the crystal holds the assembly together.

If the crystal is a tension ring plastic crystal, there is a steel ring on the inside of the crystal skirt and this assembly is forced into the case, the crystal and ring are compressed and, again, friction holds the assembly together.

2) Interference fit. This was popular about twenty years ago, but its limited water resistance has caused this method to be less popular today. In this method, the plastic crystal skirt is wedge shaped and must be compressed with a tool to be inserted into the case which has a wedge shape recess to accept the crystal. The springiness of the plastic holds the crystal in place.

3) Glue. Self explanatory.

4) Mechanical means. This covers a number of methods, usually involving a ring that is screwed or bayonetted into the case on top of or over a step in the crystal to lock the crystal in the case, usually used with a gasket under the crystal to waterppoof the assembly.
 
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