What does front and rear mean for the dial hanger?

That is a great question! I'm sorry if it's not clear in the description. 

To clarify, a "Front" or "Rear" label on a roller like this means that they're made to install on either the front closet door or the rear closet door, relative to how they're installed in the track. There are different offsets to accommodate the proper hang of each door, so that the doors can bypass each other.

Hopefully that clears things up, but please let us know if you had any other questions!