Terrible aftermarket part by Stens, will not work, do not buy!!!
Pros:
***None because it will not work as a replacement filter for Stihl 031AV chainsaw.
Cons:
***The cover that goes over the carburetor and airfilter can not be installed because the wire that it locks onto located inside the right mounting nut is too large in diameter to fit the slot on the cover's knob.
***The choke butterfly restricts the intake hole even when in the off position...
(When the choke is in the off position, the butterfly still covers the intake hole just a little bit, not much, but it should not restrict the intake hole at all. I took mine apart and removed enough material from the butterfly so that the intake hole is completely unrestricted when the choke is off.)
***The clearance holes to fit over the nuts that secure the carburetor to the chainsaw are too tight...
(It is a slight struggle to install the filter onto the mounting studs and then over the nuts securing the carburetor to the saw. It can be installed but it doesn't fit as well as the OEM fileter.)