I never have seen that thread elsewhere. The fact that TA and Herse both use 23.0 mm, which is close, but not quite the same, indicates that it is just something they made up.
A lot of the older threads are that way. When you can't find the original tool, you just make your own taps. (I once made some flat-bottom taps to retap the crank threads of TA and Herse cranks... It adds to the challenge of restoring these old machines.)
Jan Heine Editor/Publisher Vintage Bicycle Quarterly c/o Il Vecchio Bicycles 140 Lakeside Ave, Ste. C Seattle WA 98122 http://www.vintagebicyclepress.com
I have no experience of the European-metric manufacturing and threaded fastener industries.
Does anyone know if this thread size is a common size or Stronglight proprietary?
Thanks.
Richard Cielec
Chicago, Illinois