The present invention includes a hydraulic cartridge and unitary frame connection for a high pressure high temperature press apparatus with the hydraulic cartridge having a cylindrical base and truncated hollow conical section The truncated section has an external threadform with a taper between about 2.650 and 5.650 inches per foot. The unitary frame having an opening with an internal threadform extending axially substantially between an outer surface and an inner reaction chamber defined by the unitary frame and the internal threadform being threadedly mated with the external threadform of the hydraulic cartridge such that a load is substantially equally distributed across the external threadform.