A follow up question for the Expert: While waiting for your answer I used the Oregon selector guide, and it had both the 91PX056G and the 91PX057G in the list of compatible chains. But your answer to another question includes that S56 and S57 are not interchangeable. And. now I notice that in the Oregon selector guide the row for the 91PX057G is noted " Echo Brand Bars", and the 91PX056G isn't. I'll be sure and get the S57, and I am curious about what the difference is between the two chains.
Thanks for your great help. I have a lot of really big trees that are getting old, and I'm using my ECHO more and more to save literally thousands of dollars cutting up and chipping the branches that fall or that I have dropped by professionals. I'll be at this for years.