I recently decided to replace the crystal in one of my beater watches, the Citizen Weekender Garrison. In typical Citizen fashion there wasn’t any info on the correct crystal to buy. The nessesary size is 31.7mm by 1.5mm. You can find the correct crystal on Esslinger here. This size fits with the original gasket; I haven’t tested any replacement gaskets.

Unfortunately there are no fitting Sapphire crystals avaliable.