Reimal, I replaced a 31.6mm tension ring crystal on a Seamaster 30 once by heating the (empty-movement removed) case on a 60 watt light bulb and placing the crystal in the freezer for 5 minutes. The temperature differential allowed the new chilled tension ring crystal to snap into the heated case with just finger pressure with a satisfying little "snap" sound.
When the case and crystal return to normal temperature, the crystal was a normal tight fit. I'm curious if watchmakers use this hot/cold method. It seems like a lower stress way of replacing crystals.
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