What size bearings are on the 3" idler hub so that I know what size of pillow blocks to buy. Are they a universal size? or can I choose what size they can be?
8mm OD with a flange. 
Will the idler hubs integrate with any of the pillow blocks that are sold?
That would be a really easy way to get my system to integrate.
I’ve never used them with pillow blocks before.