Sorry, fletsbob - My comment was intended for Mr. dsaul, who also attempted to help. He says that the JoyTech is a "standard Shimano/Sram spline" model, but I'm not sure which of the multiple cogs on the Cambridge site meet that description. Even if I took a photo & measured what I've got, unless I understand the terminology that the manufacturers use, I may still end up ordering the wrong cog (as I've done at least three times, now, via eBay).

This is far less simple than one might suppose. Apparently, there may be multiple names for the type of hub that meets the "Shimano/Sram spline" specs. There are (for a fact) multiple cogs that look like what might fit on my hub, but actually don't. There are at least two different diameters of splined hubs (may be more) and more than one spline pattern. The possibilities seem to multiply like rabbits. Nowhere have I been able to find a table that gives all the different names of cog types and shows which are actually interchangeable.

What I plan to do is to disassemble my rear wheel, measure both the land and groove diameters, count the splines and measure the widths of the lands and grooves, and measure the thread pitch on the outside surface. I'll then e-mail the data to Cambridge and ASK what fits.

This could have been simpler, quicker, and far more obvious if only someone had taken the time to make the "cog-interchange table" that I've been looking for.

I appreciate the help, and maybe you can tell by looking at the pictures on the website which cogs will and won't fit a specific hub. My attempts have been far less successful, and it is becoming an expensive effort to buy cog after cog that won't work.

Cordially - FH