Originally Posted by trackasaurus

No. Cogs are not totally interchangeable.

I thought this awhile ago, until I picked up a cog made to precise tolerances. A british thread is "tighter" than italian thread. Most folks are running british (ISO) thread hubs : DA, suntour, formula, surly, with british thread cogs, in the rare event, some people stumble on a campy or miche cog and spin one on. works fine.

NOT the other way around. This doesn't get spoken of much as most people with italian hubs, have italian thread cogs. A british thread cog will thread on, with much force, and as a result, dull down the threads on an italian thread hub. I just picked up a used beater wheelset, campy hubs with a suntour superbe cog cranked on there. threads were chewed up and dulled from the steel cog. hub threads are almost a write off.

in short:
ISO HUB + IT COG = OK
IT HUB + ISO COG = Not OK