Am I about to wreck my nice new Pro 2 hub by fitting a Surly SS cog to it and going SS ?
I know the alu freehubs mark easily with certain cassettes but whats going to happen with a surly SS cog (prob has a 4mm base)

Help me before I make an expensive mistake perhaps……….

Your choices are:

wide base cog (which you seem to have)
new freehub body
new hub…

wide cog will probably be fine…

Surly cog with a wide base is what I use on a ProII carrier. Should be fine.

4mm cog OK on my pro 2, no marking.
Watch the chain tension isn’t too tight, that will kill it.

On-one groove armada wide based cog here. Its fine. I get more trouble from the loose XT cassette rings on my other bike.

just as a slight hi-jack, i run a steel freehub body on mine but i’ve found that i seem to go through the bearings on the inside of the cassette like crazy. They seem to eat themselves no matter what make i use. Anyone else had this? the hub was fine when it ran geared.