In the PropertyManager, click 
to
accept the mate.
The face of the knee and the face of the saddle now lie in the same
infinite plane. The mate appears in the PropertyManager under Mates.
Click again to close the PropertyManager.
To test the mate:
Click Move
Component 
(Assembly toolbar), and drag the saddle.
You can only drag side to
side and front to back, but not up and down. In some views, it might look
like the saddle is moving out of the coincident plane, but if you check
in the Front view or Right
view, you can see that it is not.
Click Rotate
Component 
(Assembly toolbar), and drag the saddle. You can rotate
the saddle only within the plane coincident with the knee.
Click .
