High pressure holders are required at forces above 2400 lbs.. Tapers are no longer practical at these levels per RWMA Manual Fig 18.3. At these high forces the electrode tapers fail because they are continually forced deeper and deeper into the holder taper. High pressure holders use mechanical attachment that mount by means other than a taper and this is not an issue.
High pressure holders come in barrel type which can be used on rocker arm or press welders. They are also offered in platen mounts for use on press welders. Both systems offer water cooling for the electrodes. Several electrode designs are availabl
Reference: RWMA Resistance Welding Manual 4th Edition