Beech Roby R-002 Help Please

[rce2]

Hi there. New to the forum. I came across half of a Beech Roby R-002 variable pitch prop. I have a couple questions about it. One, what were these used on? I read that they may have been used on WWII era L-4J Grasshoppers. Also, mine does not have a serial number. It reads "SER NO" but there is no number after that. Any idea of why this is? Above the "SER NO", it reads "DWG NO R-002-205". See pics. Sorry for the massive, sideways pics. It is also for sale, but I have no idea what to ask for it. Thanks in advance.







EDIT: Pictures re-sized, full sizes linked below:


http://i50.tinypic.com/34dfwvt.jpg
http://i48.tinypic.com/34fk1lv.jpg