Round files for sharpening chainsaw chains. 
3.2mm file fits 71 chains 
4.0mm file fits 61 and 63 chains 
4.8mm  file fits 23 and 25 chains
5.2mm file fits 33 and 35 chains 
5.5mm file fits 40, 45 and 46 chains 
 
Stihl round files can be used alone, with an added handle or fitted into a 2 in 1 chain sharpener.