my mate used to sell the measuring devices used to see how deep the ball joint goes into the bone on hip replacements and the glue the use to glue it into place

they cost an absolutle fortune but there are several different ones:
you've got your very basic ball joint that rests up against the bone
then you've got what is basicly a rose joint inside the ball to give you more flexability
then the top ones have a double rose joint, one inside the other to give you just as much flexability as you could hope for, which seem to be almost what you've got in there benni