Internal diameter is 8mm on this aluminum sealing washer. These 8mm crush washers can be found somewhere on most every Guzzi model.
Most commonly used on round head V700, 1969-1971 V7 Special, 850 GT, Eldorado, Ambassador, V7 Sport, 850T, T3, Convert,G5, 750S, S3, 850 LeMans, Le Mans II, SP1000, CX100 for the oil delivery feed lines to the cylinder heads, and the fittings for the valve cover vent lines.
Plus it's used on the bolt securing the oil filter access cover on small twins including V35, V50, V50 II, V50 III, Monza, V65C, V65SP, V65 TT, Lario, Nevada, Nevada Club, Florida, V7 Classic, V7 Racer, V7 Racer II, V7 Cafe, V7 Special, V7 Special II, V7 Stone, V7 Stone II, V7 Stornello, V7 Racer III, V7 Special III, V7 Stone III, V7 Aniversario III, V7 III Carbon Dark, V7 III Carbon Shine, V7 III Rough, V7 III Milano, Breva 750, Nevada Classic IE, V9 Roamer, V9 Bobber.
These are a common, universal crush washer, also used on many models of Honda, BMW, as well as Ducati and other Italian makes