Re: [CR]An answer to: ISO cog threading on a track hub?

(Example: Framebuilding:Technology)

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Date: Mon, 12 Sep 2005 13:29:28 -0400
From: "Sheldon Brown" <>
Subject: Re: [CR]An answer to: ISO cog threading on a track hub?

Kristopher Green wrote:
>Last week I sent a desperate email missive requesting information on
>why a NOS Gipiemme track hub I'd had built up that was stamped
>"Special ISO" permitted a standard Suntour cog to be threaded on by
>hand, but allowed that cog to spin impotently across the threads the
>moment leg power was applied.
>Thanks to those who replied, but the correct answer actually came from
>my local mechanic, framebuilder Bill Stevenson, who is a great source
>of wisdom, a good friend, and the anchor for our local road riding
>scene. Like me, he found nothing online, but an old Sutherland's
>manual revealed that the ISO standard did actually differ from
>longstanding cog threading conventions. In this case, ISO adopted the
>same pitch and diameter as that used for French bottom bracket cups.

I don't believe that's correct.

My 4th and 7th edition Sutherlands' agree that ISO DIS 6698 specifies 1.375 (34.92 mm) x 24 tpi, 60 degree. This is for freewheels, but there is no separate listing for fixed sprockets.

This is the same as the ISO DIS 6696 standard for bottom bracket threads.

Old English standard is 1.370 (34.80 mm), 5 thousandths smaller. This is not generally enough to matter, but if that was the nature of the mismatch it would make an English sprocket a slightly tighter fit on an ISO hub.

French bottom brackets are larger, 35 mm (1.378"), with a slightly finer 1 mm (25.4 tpi) pitch.

If the hub was this size, you wouldn't be able to fit an ISO or English sprocket onto it.

I think the hub was marked "Special ISO" to distinguish it from the obsolete Italian size, 35 mm x 24 tpi.
>Longtime shadetree mechanics will recall that English cups will thread
>into French BB shells pretty nicely

English inside, French outside...that can "work." French inside, English outside, no go.
>(the cog went onto my hub like it
>was buttered), but that they won't stay put in use.

do the threads on the hub run pretty much all the way to the shoulder? Sometimes you can run out of engagement on a hub because the threads usually stop somewhere short of the shoulder. This is more often a problem with low-quality, thin stamped sprockets.

Given the general quality level and reputations of the brands involved, my guess is that the Gipiemme hub is defective. This is not a brand noted for quality.

Sheldon "ISO" Brown Newtonville, Massachusetts

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