mike,
GB stands for griffiths-beerens. they are an austrillian made bar and seem to take the high rpms and last a long time. i have never hade a problem with these bars and i use many of them. for what ever reason i replace a bar these are what i use. this is mostly what i stock too. if for some reason i have another bar in stock it is because i got a saw in that i did not want that size bar on it and it got replaced from day one. protect yourselves; marty