Ballscrews from Steering boxes

Just caught up on the digests (finished digesting) after being away a lot.
In one of the posts that someone mentioned that ballscrews are used in most
automotive steering boxes. Could someone elaborate on their suitablity for
use in CNC conversion of small drill/mills?

I presume that the actual lead screw in the steering box is too short to be
useful, but are these mostly normed threads, so that you could get a
standard ballscrew threaded rod from an industrial supplier and use it with
the Automotive recirculating ball nuts?

Are the nuts of high enough quality to be of interest?

Mark Wrathall