Leaderboard

Pretty sure I've seen these before on barrels on other bikes, I think their purpose is to centralise the long studs through the barrel, so the barrel fits correctly, as you first tighten the nuts up, they press into the top of the barrel and stay there. If the barrel is stripped/sand blasted and the like then you'd probably have to replace one or two. In the distant past studs that went through drilled barrels suffered from corrosion and you could never get the barrel off, these centralising washers (sacrificial as Snake points out) keep the studs in the correct place and the studs exposed between the cooling fins but not corroded onto the barrel but more importantly centralising the barrel and cylinder head.