Actually, only three Cycle (CEI) threads are 26TPI. Smaller than 1/4" are finer and larger than 3/8" are coarser. You find quite large diameters with TPIs of 26, 28 or 32 but they are not cycle threads. Whitworth was not used much on cycles although it is on some older bikes. More usual would be BSF which used the same spanner sizes. 1/4 BSF is 26TPI. British Standard Brass used 26 TPI from 1/8" up to over an inch. Anyone without a lathe was quite likely to use BSB dies as they were so widely available. I have found 26 TPI on a French motorcycle and on the fuel tap threads of Italian motorcycles. I wonder why 26 was a magic number.misguided attempts to
Because of misguided attempts to standardise simultaneously with two continents, there was a time when British Fords needed spanners for Whit/BSF, UNC/UNF and Metric!
Stuart Tallack in West Sussex
Mark Stonich wrote:- British bike threading is NOT Whitworth!!!! (*)
This is a common misconception, because many 26 tpi BSC fasteners had the same nut and bolt hex sizes as Whitworth threaded fasteners so Whitworth tools fit.
26tpi is BSC British Standard Cycle. In most sizes this is a rather fine thread, intended to avoid loosening from vibration on cycles, motorized or not. Whitworth is a much coarser thread, same pitch as UNC in most sizes but with 55 degree threads vs, the 60 degree threads of the BSC and UNC.
I wonder if the 10mm x 26tpi Campagnolo axle threading had something to do with buying British lathes, surplus from the cycling industry, that would only do 26tpi.
Another possibility is that older eyelet threads are the coarser, pre-ISO 5mm x 0.9mm. Mostly on French bikes but IRRC the Campagnolo 1060 dropouts on my Jack Taylor are 5mm x 0.9mm. Screws from old French derailleurs will sometimes work.
(*) There are no absolutes when talking about the British cycle industry so I imagine somewhere, somewhen, something with Whitworth threading was used, but I've never heard or seen of it happening.
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