The BCD of a NR Triple is 100 mm. Knowing the bcd doesn't really help much because only campagnolo mass-produced rings and in their infinite wisdom, campagnolo only bothered to make a 36H ring (as far as I know.. anyone?) In that sense, this is the most useless triple in the history of triple chainrings.
Luckily, there are alternatives. If you can find a used jim merz chainring, I think he made 31T and 32T rings. I talked with jim about a year ago and even sent him my NOS campy ring as he was going to use up his stock of rings with the spider not-yet-machined out. However, due to a lack of time he shelved the project and sent the ring back to me.
I have purchased some OFMEGA rings (35T, 36T) which are 102 bcd. Since the diameter is only 2 mm bigger, this means that you can grind 1 mm out of each bolt hole to get a 100 mm ring, and this is often done in off-by-2-mm situations (i.e. I've heard that some have had success adapting 130 bcd shimano rings to 128 bcd nervar cranks using a similar trick.)
- Don Gillies
San Diego, CA, USA