If you're upgrading the crystal on your watch to one of our sapphire crystal options, it's perfectly fine to re-use the crystal gasket that came on your watch.If you're starting a watch build from ground up (ie. purchasing all parts individually), you'll need to be sure that you have a crystal gasket. If you need to purchase a crystal gasket separately, we do sell these (under our "Tools & More" section). If you're purchasing a watch case from us, we bundle it with all necessary gaskets, including the crystal gasket.