12" Stihl Genuine Chain For Stihl MS 171 / MS 172 44 links of 3/8 Hobby 

Count the number of drive links in your old chain to determine your chain length. SEE SECOND PICTURE.

The drive links are the bottom parts of the chain that sit down into the guide bar.

Take chain off chainsaw, lay flat and count the drive links in 2's e.g. 2,4,6,8,10 for the easiest way to find you chain lenght.

Stihl Genuine Chain

Chain Specification
Bar Length: 12" (44 Links)
Chain Pitch: 3/8" Hobby
Chain Gauge: .043" / 1.1mm
Chain File Size: 4.0mm / 5/32"

FITS:

Stihl MS 171 replacement chain

Stihl MS 172 replacement chain