Oregon square ground chain [This is the full skip version] – 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. Almost impossible to source in the UK – we try and stock it but it is expensive to get in and can run out of stock for a few months at a time.
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.