This Vstack adapter fits the low top intake elbow only. It will not fit the high top intake elbow sometimes found on the 281/288 Husqvarnas. The 181 came as a low top only.
When you install this Vstack adapter, use the supplied nuts to secure it to the stock intake elbow. You can then fit any 2" I.D. air filter you'd like. I recommend a foam air filter, such as the Red Beard Saws Air Filtration System, or a PK-82, or the Green Weenie.
This Vstack adapter will also fit other chainsaws, such as:
Husqvarna 61 and 266. (Please check your intake elbow, some of the older 61's had a first gen intake horn, made of aluminum)
This Vstack adapter will also fit some of the older Pioneer chainsaws, You would need to source a Husqvarna 288 low top intake elbow to make this system work on your Pioneer.