Match the file to chain pitch, not the gauge

Picking a 5/32” vs 3/16” round file comes down to your chain’s pitch, and drive link thickness has almost nothing to do with it.

The 5/32” file is for 3/8” low-profile chain — the stuff on most homeowner saws — and also for 1/4” pitch chain. The 3/16” file is for .325” pitch chain, which is common on mid-size saws. If your saw is a typical Stihl MS 170 or similar, you’re probably on 5/32. If it’s a bigger .325 saw, grab 3/16.

Drive link thickness gets confused with this because people see numbers like .050” and .058” stamped