Speedometer drive clamping spacer/washer. Made in the UK. Replacement for Ducati original. 

a/  Made from tougher and non corrosive material (stainless) to stop it seizing onto the spindle.
b/  Increased thickness (1.45mm) to stop dishing, and becoming ineffective as a clamp for the drive unit
c/  Essential part if the speedo drive unit is to work, and not destroy itself
d/  Fits the disc braked singles as well as all the bevel v twins, and the 500/600 650 Pantah & Cagiva 650 ala azurra and early 750 F1