So I read this and another post on here somewhere about not being able to use one on a hub after you have used the other, say a BSC on and ISO hub so that you can only safely used BSC cogs from then on out. Is this correct? I have formula hubs and have been using a Dura Ace cog but want to switch to a higher tooth count and EAI has the one I want. The DA is BSC and the EAI is ISO and I am assuming the formula hub is also ISO. So any thoughts on this?

EAI cogs thread profiles are little bit thicker than Dura Ace I think, and they go on Phil hubs are little rougher; it may be the other way around.

They are all ISO though, just different in thread profile.

the guys in the other post was talking about the cog trimming a little bit of the peaks of the hub threads and narrowing the profile a little. I just cant remember if it was the DA cog being BSC that did that. Unless the DA is ISO too.

Originally Posted by Baxtefer
Type Thread Equivalent
I.S.O. 1.375" x 24 tpi 34.92 x 1.048 mm
British 1.370" x 24 tpi 34.80 x 1.058 mm
French 34.7 x 1 mm 1.366" x 25.4 tpi
Italian 35 mm x 24 tpi 1.378" x 1.058 mm

and

ISO, English and Italian are all semi-interchangeable, but it you shouldn't go back and forth between different types of freewheels on the same hub repeatedly

I'm not sure I'm following what you're talking about but here's something that could be useful that I found from my fixedforum.

The lockring threads are the ones that are generally called Campy/Phil or DA, etc. Their diameters are quite different. Cogs on the other hand, should all be 1.37" x 24tpi (with the exception of some true oddballs like the French thread). The tolerances to which they are manufactured however are slightly different. I don't have a stack of hubs available, but I do have several brand new cogs. The inside thread diameter of each is as follows:

EAI = 1.330"
Campagnolo = 1.330"
Dura Ace = 1.336"
Phil Wood = 1.334"
Steelwool = 1.328"
Miche quick change = 1.332"

Bear in mind this is across the inside of the cog threads, so it is not the nominal 1.37" that is their specification (and would be the measurement across the hub threads). However, it does give some insight into why an EAI cog is a tighter fit compared to a DA cog, as would the Campy cog. That extra few thou of interference in the thread could be a problem on some hubs. They are all 24tpi thread pitch. I have put a Steelwool cog on a Miche hub with no issues, but that is only a .004" difference and it didn't spin on as easily as the Miche quick change carrier.



Not many track hubs are French or Italian threaded, most of them are ISO.

you fund more or less the same stuff i did... so as was said I just shouldnt switch back and forth a whole lot...
man really shimano you couldnt just start making a few bigger sizes!! only reason I am going with a EAI is they have a 17t...

According to Southerland's, BSC (English) and ISO freewheel / cog threads are a Class A fit, which means that they are interchangeable. This is because, although there are very slight differences in dimensions, they are less than the clearance differences between the dimensions of the external threads on the hub and the internal threads on the freewheel / cog. Threaded parts such as nuts and bolts are not meant to be interference fits, which means that there must be a small amount of play in the connection until it is completely tightened. A BSC cog on an Italian threaded hub is a Class B fit, which means that it will work and be serviceable, but will damage the threads slightly. Bottom line, don't lose any sleep over using BSC or ISO cogs on the same hub. Oh, and Soma makes excellent cogs from 16T thru 22T in 1/8" thickness for a lot less than EAI.

ohh Southerland's, I really need a copy of that beast! On the matter of cogs, I really really love my DA cog, and all I have read says EAI is the next best (and not the $60 one either). I had read some kinda blah reviews about the Soma ones, though, that might have been the ones with all the holes i them... I just wish bens cycle still had free shipping LOL...