This 20mm (ID) aluminum sealing washer is used in some capacity on nearly all Guzzis from 1967 until 2016.
It is commonly used on the Big Block 750, 850, 1000 and 1100cc engine oil drain plug, but is also used on many engine oil fill or dipsticks, and on many those models for the transmission fill and rear (final) drive fill plug.
Front engine drain plug washer for Small Block V35, V50, V50 II, V50 III, V50 Monza, V65C, V65SP, V65TT, V65 Lario, Nevada, Nevada Club, Nevada Classic 750IE, Breva 750, V7 Classic, V7 Cafe Classic, V7 Racer, V7 Stone, V7 Special, V7 Racer II, V7 Stone II, V7 Special II, V7 Stornello II, V7 Racer III, V7 Special III, V7 Stone III, V7 Anniversario III
It's best to use a new one of these crush washers at every oil change. Replacement for the old number fiber washer 90714195.
It was also used on the V700, Ambassador, V750 Special, 850GT and Eldorado in the cylinder head, to seal the 12 o'clock cylinder stud access plug.