1/8,
See this thread:
http://www.bikeforums.net/showthread...ghlight=riggio
The nice folks at this website have created a repository of many bike catalogs. However, the Riggio catalog in this site doesn't have the model frame that you/we have.
http://bulgier.net/pics/bike/Catalogs/riggio/
Riggios were made by Viner.
The bike frame in the your photo looks exactly like mine but mine is cobalt blue. My frame is Columbus SLX and the rear brake stay comes to a point right above the hole (I don't know how else to describe it)
Hope this helps