Acme nut question

[SPEEDRE]

I can't remember where I saw it, but, the nut was driven by the motor and the screw seemed to be attached hard to the Z. Can anyone tell what this nut is called. I think I might like to use one for my upcomming conversion.

[the_ball]

Here is such a setup: http://www.homecnc.info/cncparts.htm

I think this is a normal ballnut though.