Measuring at 4" in diameter, these silicone rubber seals are meant for use during vacuum/centrifugal casting in order to seal the perforated casting chamber and flask ring. This gasket item acts as a sealing layer between the hot flask. The casting chamber flange adapter provides a tight seal, therefore allowing the vacuum to entirely pull the molten metal into the flask. Please contact us with any questions. Please visit our store for other great jewelry tooling items such as; Hand Stamps, Disc Cutters, Polishing Compound, Buffers, Hammers, Tweezers, Mandrels, Anvils, Vises and more! Thanks for Looking!