fulcrum pin engineering question

I do not understand why the fulcrum pin needs to be threaded at all?  If
grease impregnated bushings were pressed into the A-arms and king pin, why
couldn't you use a hardened non-threaded pin, and allow free movement at all
three points in the outer assembly.  A circlip could be used to keep the pin
from falling out, or fit a bolt to the narrow end.
David Riker
74 Midget
78 Midget
63 Falcon
http://personalweb.sunset.net/~davidr