fixiefix

Hello and Merry Xmas / Happy Holidays to all my fellow cyclists and fixed riders!! #fixedgang

New member here but not new to cycling. Problem is I've bought a somewhat rare item from Ebay in the UK. It is an 18T fixed/track cog with an antiquaited 3/16 tooth profile for extra-wide chains, but unfortunately it doesn't fit on my track hub or on any other threaded hub I've got. The cog's threads are slightly too large to engage with any of the hub's threads. It will rest/hang loose around the hub's threading, looking as though it is installed but actually it isn't. At a glance the threading looks the same as on my other track cogs but when put side-by-side it appears to be a millimeter or two larger in thread diameter than the ISO (1.375 x 24 tpi) threading of my other cogs. There is a tiny mark stamped into it but it is hard to make out. PB, PG, P6, PS or P8... something like that... I have searched Google for clues to its providence but alas haven't managed to find anything like it. It is made of steel, is slightly rusted and appears to have been used although the condition is remarkably good. The seller had it listed as 'New Old Stock' but the traces of grease on it show it was surely installed/used at some point. The other oddity is that the threading on it is very shallow - the threads are ~1mm in size, but there appears to be only 2 or 3 threads on there! less than half that of my other cogs.

I may eventually end up returning it to the Ebay seller but I would like to know if/how it can be used, if anyone knows. I am happy to add some pictures and attempt to measure the thread diameter (with a simple ruler of course - in the absence of any more-precise instruments) but I don't think it will give any more clues beyond what I've described thus far.

Thanks for reading and any help is greatly appreaciated.

TugaDude

Pictures would help. Personally, I would return it. Why mess with it? There is a chance that it is a proprietary thread or perhaps Italian. British and ISO are virtually identical, so that isn't the problem.

Depending on how old it is anything is possible.

TejanoTrackie 

It won’t be Italian, either. The difference between Italian and English or ISO is very small, and an Italian cog is a B fit on an English hub. Specifically, the thread diameters for the different standards are as follows:

English - 1.370” (34.8mm)
ISO - 1.375” (34.92mm)
Italian - 1.378” (35mm)

The thread pitch is 24 TPI for all three.

Ref. Southerland’s Handbook for Bicycle Mechanics, Third Edition.

veganbikes

Post some pictures. I personally wouldn't want to run super vintage fixed gear stuff unless it was original to the bike and I was doing some sort of L'Eroica event. If you can return it do so if you can't keep it in the bin or on a shelf to look at.

fixiefix

Here are the pictures finally, apologies/thanks in advance for your patience I have not attempted to measure thread diameter with my ruler but would estimate it to be equal to or greater than 36mm but not more than 37mm. For comparison I have photographed the cog beside a regular 18T 1/8" track cog (which I believe to be ISO/1.375")

Hard to capture with fixed focus. PB perhaps but I'm not certain. At other angles it appears more like PG



Hangs lower both top and bottom, but this angle still doesn't show the very bottom teeth, see last picture. Also you can vaguely see the edge of the threading on the right of the cog







oddly shallow threading compared to the 1/8" cog



>2mm lower at the bottom, perhaps even 3mm

TugaDude

Those are monster teeth. The width of the teeth wouldn't work well with modern chain I don't think. Back in the day there was a 3/16" wide chain, so perhaps that cog is to be used with the wider chain?
If you want some classic and vintage folks to look at it, post if on the C&V forum. Amazing amount of knowledge over there.

TejanoTrackie 

I'm not sure that's even a proper bicycle wheel hub cog. For one thing, it lacks any flange at all, which is why it has so few threads. For all I know, it's used on some kind of chain driven machinery. Even pre WW2 bicycles adhered to the hub threading standards of today, the largest diameter being Italian, which is smaller than what you have. As suggested by others, you might try re-posting in the C&V forum to see if they can identify it, but even so you won't be able to use it. I recommend returning it to the eBay seller.

Mad Honk 

I suspect this is from an early threaded freewheel that accepted 3/16" chain. I would stay away from trying to use it as a track ring, it may do more damage than good. Track rings are available elsewhere,I would send it back to the seller. Smiles, MH

79pmooney

That would make sense. The freewheel body would be steel, so fewer threads would be needed.

Gsichta

This is a thread-on cog for coaster brake hub. American coaster brake (and some fixed) hubs used this style on 28” singletube and 26” ballooner bikes from about 1910ish - 1950s. Manufacturers like new departure or morrow. It would be more common in a 1” pitch. 1/2” pitch would likely be after about 1935, if it’s an American cog.

Im sure were uk/European coaster equivalents from that era...