I am not sure if this question can be definitively answered and searching the threads has not answered my question.

I picked up a Bianchi Nuovo Racing 12.V several months ago. Best I can tell it is a 1982 model with the serial # 2M1271. The sprockets on the freewheel are pretty well worn out so I need to get a replacement. Currently it has OfMega hubs and a sach-maillard freewheel, six-speed, 13-26 (by what I've read it is may not be original).

Does anyone know what the proper thread size is for this combo? Or is there a way to look on the freewheel to tell. At this time I have not removed the freewheel from the hub but will probably go have that done this weekend.

Thanks
Doug