I checked 8 or 10 fastner houses I've used in the past and not one of them has anything in 23.5mm. I think Porsche may have used this thread on some engine parts, but that's as close as I came. I think I could have a run of extractors made up if enough people were interested. I have no idea of the cost but I wouldn't charge any markup, other than keeping one for myself ;<). I doubt the machinist I work with would do it if there were less then 30 or 40 orders. I'd also need someone to lend me one for a pattern.
> 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
> Vintage Bicycle Quarterly
> c/o Il Vecchio Bicycles
> 140 Lakeside Ave, Ste. C
> Seattle WA 98122