Load-Carrying Type
Load carrying ball joints can be divided into two types. In the tension-loaded type, forces applied to the joint housing are pulling the stud against the housing. In the compression-loaded type, the same forces are pushing the stud into the housing. The tension-loaded is the more popular design.
The catalog will list vehicles that have four ball joints. If you are replacing the lower ball joints, it’s a good idea to check the uppers. NOTE: Never order a ball joint based on its size alone. Ball joints of the same size may have very different, application-specific engineering. Installing the wrong part could cause safety issues for which you could be liable.

These are from the MOOG pages,
The 818 is Load carrying in the tension loaded type, and so what if it is the more popular design, the main concern in the 818 is... Was this Subaru ball joint which is a following type initially from Subaru, engineered to be used in a tension load? I think NOT.

Can the engineers at FFR shed a light on this design decision? Thanks Don