I have 5 double row AC bearing here and all have around .0015" of end play.
They were not OK for ballscrew supports, preload or zero clearance is necessary.
Preload can be specified for a bearing or liner rail.
This is the preload chart for some liner rails.
Hiwin linear bearing preload classifications
If the double row AC talked about in the first post has some preload and is made for spindle use it would be of great use to many to throw together a nice second spindle or rotary table or the like. That is why I asked for the specifications because I have not seen them before.
The bearing is either pre loaded or it will have slop when in use as a spindle bearing.
If pre loaded it will be stated in the specification.
If not stated it will have slop.