I've some the same as Fazersharp, they're one of the genuine Yamaha models. I can attest they work, have saved my engine several times after binning the bike. They usually bend up a bit and/or get dented. Rubber mallet can sort them out from a minor off, but still fairly sacrificial from a bigger off. Rather replace one of these, then half the engine and not be able to ride home... On the track I can usually get within about 0.5 cm of tyre limit (Metzeler Z8's) have yet to grind them. Have ground pegs before these mind.