If you're talking about #3 in the diagram below then you have to buy it as a set with the shaft etc., pre 03/2002.
RealOEM.com * BMW E53 X5 4.4i STEER.COL.-LOWER JOINT ASSY
If your X is pre 03/2002 don't try to save money or time and get the later date joint as a separate piece it will not fit...I know this from experience.