Yo dudes,

So I got an 18t Roselli cog today, to put on my Zeus rear hub. The threading on the cog is 1.37 x 24TPI and I was assured the size was correct by a suitably reputable source (Shifter Dan).

The problem is this: When I start to thread it on, I get about half a turn in and it catches. I put a little pressure on it with my chain whip, thinking there might have been a minor deviation in the threading or something. Problem was, it didn't get easier to turn.

When I removed the cog, it looks like it's eating the hub threading alive. Nasty burrs and bit of metal coming off. It's only on the start of the hub threading, as I didn't go any further than that, so I haven't trashed the hub.

I'm guessing it's not really a good thing, but this is the first fixed gear I've built so I'm no expert on the matter.

Am I doing it wrong?

Any help is much appreciated, cheers.