Oregon square ground chain – square ground chain is the highest performing chain there is with very fast cutting and good stay sharp properties. 15% to 20% faster than standard full chisel.
The disadvantage is that it is very hard to sharpen correctly – a very different technique is used with a special (and expensive) type of file.
Using the Granberg clamp on file guide is essential for getting this type of chain sharpened right as then you can set and duplicate the complex angles. There is an excellent guide on how to do this here. If you are serious about square ground chain you need to read it.