Match your chain to the correct round file diameter, filing angle, and depth gauge setting.
File every cutter with the same number of strokes. Check depth gauges every 2 to 3 sharpenings with a flat file and gauge tool. When cutters are filed back near the witness mark, replace the chain.
| Pitch | Round file | Metric | Common chains |
|---|---|---|---|
| 1/4″ LP | 5/32″ | 4.0 mm | Oregon 25AP, carving chains |
| .325″ | 3/16″ | 4.8 mm | Oregon 20/21/22, Stihl 23/26 RS |
| 3/8″ LP | 5/32″ | 4.0 mm | Oregon 91, Stihl 61 PMM3 |
| 3/8″ | 7/32″ | 5.5 mm | Oregon 72/73/75, Stihl 33/36 RS |
| .404″ | 7/32″ | 5.5 mm | Harvester and large saws |
Your chain pitch is stamped on the guide bar or printed on the chain box. If you only have the chain, measure the distance between three consecutive rivets and divide by two. The Oregon 90PX is the odd one out: it takes a 4.5 mm file that nothing else uses.