Stihl Duro Tungsten Chain 18" 26RD3 .325" .063 68DL

If you hate stopping to sharpen your chain then this could be the answer with the Stihl Rapid Duro holding its edge for up to 4x as long as a standard chain.

A special carbide-tipped saw chain that remains sharp for a very long time in frequent use and, above all, in extreme conditions (such as when cutting dirty or frozen wood and in demolition work)

You require a diamond wheel to sharpen these and cannot use a conventional file. 

Drive links: 68

Pitch: .325"

Gauge: .063

NOTE: Tungsten, although holds it's an edge for longer than a standard chain it is more brittle. Meaning it is common for you to break tungsten teeth off if you hit something with the chain completely rendering it useless.