Distributor points to points-plate hold-down screw
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
The little screw that secures the points to the points-plate is 3.5 mm wide × 0.6 mm thread pitch × 4 mm long.
A suitable replacement is McMaster-Carr part number 91800A175. It is 6 mm instead of the required 4 mm length (a shorter version is not available from McMaster-Carr). You'll want to file off the extra 2 mm so that it won't interfere with parts beneath.