Distributor ball bearing
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
There is a tiny little spring loaded ball bearing used to make contact between the advance plate shaft and the main shaft that is connected to the gear. The size of this ball bearing is 3.175 mm or 0.125 inch or 1⁄8 inch.
A suitable replacement is McMaster-Carr part number 9528K11.