Q: Did Rudge Whitworth invent the Whitworth thread?
A: No, there is no connection. The Whitworth thread form was invented by Sir Joseph Whitworth in 1841 and by 1860 the thread was in universal use in Britain and the USA - Source Biography titled 'Sir joseph Whitworth, the world's best machanician' by Norman Atkinson (acknowledgement to Stewart Wilkins).
Q: Why are 2 of the rivets holding clutch friction discs closer together?
A: When looking at modern reproduction clutch friction rings for Rudge clutches, 2 of the rivets are closer together as in the picture.
This feature is a left over from when RW manufactured the linings by forming them from a strip into a disc. This process meant that the 2 ends of the formed ring needed to be joined and RW did this by 'stitching' the 2 ends together using copper wire. To support this inherant weakness, RW placed a rivet either side of the join. No longer required today but the rivet holes are there!
Q: What is the groove under the filler of my gearbox for?
A: This indicates that the gearbox has come form a 1934-36 machinefitted with a mechanism shield. The shield is a tight fit and often rubs a mark into the underside of the filler. In severe cases the shield can wear through the filler with a subsequent loss of gearbox oil!