I just received a brand new EAI 18t track cog from Ben's cycle. It's for my Campy Nuevo Record track hub. The problem is that it only goes half way in and then gets stuck. I've compared with the 14t Campy cog that originally was on and that spins on smoothly all the way. What's wrong here? I know cog threading is (almost) universal so where's the problem?

The EAI campy lockring works fine by the way.

Should I force the new EAI cog on from the halfway position or do I risk breaking the threading then?

Aren't campy hubs Italian threaded or something?

do NOT notnotnot force the cog on or you will strip the threads. that hub needs a campy or phil cog.

1) Do not BLINDLY force on the cog. Check out its threads, see if there is a burr or other problem with them.

2) While there are 3 Major different thread standards(+French), they are similar enough that people swap between them without major issues.

3) Lockring threads are where there is the drastic difference between "regular" and Campy/Miche/Phil.

i thought that lockrings had different threadings and that cogs all shared the same threading

Yeah, that's what I thought also.

from the phil catalogue

"The use of “stamped” or plated cogs with minimum thread engagement and beyond normal spec thread tolerances are not recommended with quality track hubs. Our thread is 1.370 x 24 tpi. This is compatible with most high quality cogs. Caution should be taken with some cogs marked as ISO thread – the pitch may actually be closer to 1mm than to 24 tpi. A simple test is: Thread the cog onto a quality freewheel type hub. If it easily threads to the freewheel stop, it’s 24 tpi – if it jams before, it may have a metric or other pitch – NOT COMPATIBLE with ours and other quality track hubs."

This should be a sticky.

Cog threads can be French, ISO, or BSC (British). French disappeared from the scene 40 years ago, so you don't have to worry about them on any modern hubs. ISO and BSC are similar, but not quite identical. In particular, they differ in the depth of the threads, so mismatching can cause you to shave off the tops and a bit of the sides of the threading on the hub. If you (or somebody) has already done the mismatch, then you've already shaved the threads slightly so yes, the wrong cog will spin on just fine. You have just increased the risk of stripping somewhat.

To add to the problems, some cogs are subjected to hardening treatments that gunk the threads up with stuff that prevents them from fitting properly (Suntour Superbe Pro cogs are particularly bad at this). If you use a brass brush and clean out the threads, this problem goes away. Oh, and you can have a ding on your cog threads which can prevent it from fitting any hub properly without messing up the threads.

On to lockrings: There are three versions, Campy, BSC (English) and Mavic (French). The Campy lockring works on Campy, Zeus, Gipiemme, and the various Campy clones (and on Phil Wood, by the way). BSC is ubiquitous on all the Japanese hubs and most others. Mavic is unique to Mavic and is almost, but not quite, a BSC thread -- some people use a BSC (Dura Ace) lockring in a pinch and since you aren't torquing it like a cog, you might get away with it, but Mavic lockrings are cheap and readily available from John Dacey at Business Cycles.

Hmm.....I have 2 sets of Nuevo Records and all my EAI cogs spin on without much resistance.

I have an EAI cog on one set of my Campy hubs -- threaded on no problem. I'm not sure what was on it before since that pair came sans cog. The other set I have has a Campy steel cog which also works fine. I don't remember if there was any resistance aside from the usual grittiness of old hubs that have been used but if it really feels too tight then don't. You may also want to clean the threads out to make sure there's no grit or sand or whatnot.

As for cogs, ZappCatt has it right - Marcus at Yojimbo's said there were no issues with EAI cogs on Campy hubs so I went with that over Phils or whatnot. I brought this up in the for trade thread I believe and it came out there there are differences. I think that if you thread on a certain kind of cog, make sure it's that threading from there on out.

Should I try to "clean" the threads on the new EAI cog from the supposed hardening treatment then? The bad part is that I'll ruin any chances of getting a refund.

Gentle cleaning with a wire brush wont negate any return/refund.
Ben's is cool. Just call them up and tell them what's going on.

Anybody using one of the new Surly cogs on an old Campy hub? I threaded one on at the shop last week and it went on without any problems, but I'm still kind of worried about using that combo.

If it comes on smoothly then I don't see why you should worry.

I think I remember the cog "catching" slightly at one point, but it didn't take any force to keep threading it on. Might be due to a burr or something on the threads?

I guess I'm just really paranoid.