There's a wonderfull book out there called "Six Days of Madness" describing, mostly, pre-WWII 6-day races.
One of the things you eventually notice, paging through the photos, is that many of fork crowns on the bikes were Single-Plate like the one for sale now on ebay (130230623747) at:
http://ebay.com/
When did these go out of fashion and why? Were they ever used on road bikes?
Amir Avitzur
Ramat-Gan, Israel