Does anyone know what pitch thread in the center of the knob is, I know it's 3/8 diameter, but is it cycle or BSF. Cheers............Greg.
The one's I have with evidence of black paint are 3/8"BSF.
But a pair of obvious shiny reproduction ones that I picked-up in the US years ago are UNF!! Ugh!
This leads on to some other issues regarding spring-box fasteners. Referring to Bill Parr's Series A Spares List on Pages 46/47;
1. Don't forget that the F94B bolt, that the brass knobs screw on to, has a rounded head (slightly domed) to stop people trying to turn it with a spanner. This is important because just under that head, and touching it, is a transverse steel pin pressed-in to prevent the bolt from turning with the brass knob. For reference the bolt is 2-1/4" long (under head) with 1-1/4" of thread.
2. The late great Bob Stafford told me there are were different materials for the spring claws (e.g. mine are Al Alloy - but it is a TTC
) and different threads in them from 1933ish to 1939. The Bill Parr listing shows the corresponding "570" thin nut on the spring eyes as 7/16 CEI (which means it is not a post-war BSF "570" then!). I've not seen a 7/16 x 26 CEI spring claw but mine are quite clearly 7/16 x 20 Whitworth-form threads (on a std Whit hexagon) - the 20tpi's being a derivative of the CEI offerings. (I made up a small batch in SS if anyone finds they need a set).
The post-war Vincent guys really don't know just how lucky they are by having every last detail of their machines fully documented, part-numbered and available!!! That said, there's nothing better than a challenge to keep the grey matter functioning....
Peter B