Disclosed is a threaded safety cap for a high pressure, high temperature filter press. One disclosed filter press includes a cell having an open end, a cap configured to be threadably coupled to the open end and comprising a retaining ring defining a central orifice and a cap seal having a longitudinal extension configured to extend through the central orifice, one or more filtration components, and one or more seals, wherein, then the cap is threadably coupled to the cell, the cap secures the one or more seals and the one or more filtration components within the cell.