Screw for CEV semi-round, flat sided tail light lens 14741701. Diameter of threaded section is ~3.9mm, overall length is ~74.66mm, and the head diameter is ~6.6mm. There has been several variations in these tail lights over the years so be sure to measure what you need prior to ordering.
Fits tail lights with original Guzzi part numbers 17741701,14741700
Used on Guzzi, Ducati, Laverda, Morini, Harley/Aermacchi, Piaggio, Vespa, Garelli and no doubt other small displacement Italian bikes, scooters and mopeds.