Thread inch confusion...

So I decided I could stretch to a new hub on the back for my wheel build and I got myself a new Novatech one ( https://www.sjscycles.co.uk/hubs-other/novatec-fixed-free-rear-hub-black-32-hole/ ) As it already came with a lockring, new bearings etc.

It says it needs a cog which is - 1.37" and 1.37/1.29". I'm assuming the first 1.37" is the freewheel side and the 1.37/1.29" is the fixed cog and lockring accordingly.

Looking at some fixed cogs such as this: http://www.wiggle.co.uk/brand-x-13t-20t-fixed-gear-track-sprocket-18/ they are down as 1.375" Is this the same and Novatech have just rounded the number down or is it a totally different size? I don't want to end up stripping the thread.

Many thanks

Paul

I think 1.37 is both the freewheel and fixed sprocket thread size and the 1.29 is the lockring.
I've never ran fixed but I've read and been told that you can run a freewheel on fixed/free hub so the the thread size must the same in both cases.

Theshipwright is right :) 1.37 X 24 is also the standard thread size for English bottom brackets...

Thanks guys, so is there no difference between the 1.37 and 1.375 cogs?

It's the difference between British standard and ISO standard: http://www.bikeraceinfo.com/tech/bottom-brackets.html

Or look up Sheldon Brown's writing on the matter.

@paul8vv yes there's no functional difference as it's so small, it's a thousandths of a mm.

Ah okay. Thanks everyone. I thought it was a bit odd there would be two standards that were so similar!

Much of the ISO bike standard is based on BSC.

Although single speed freewheels, multispeed freewheels and fixed cogs all
share the same thread and can swapped about, should you so desire, bear in mind there are 2 different standards for lockring threads. From Sheldon;

Fixed-Gear (Track) Hub Lockring Threading (Left-hand thread):
English/ISO 1.29" x 24 TPI
Campagnolo/Phil Wood 1.32" x 24 TPI
(Old French 33 mm x 1.0 mm)

Ah yes, thankfully the novatech comes with a lockring but I know they always get chewed up so I'll no doubt be replacing it at some point!