In most mini split installations a hole is drilled through the wall to run the refrigerant pipe, drain tubing and 14/4 stranded wire through. The wall sleeve is installed through that hole with the flange side on the exterior side of the wall. This helps to seal the openinig and provide a cleaner installation. 

This wall sleeve is part of the DiversiTech SpeediChannel™ line - an innovative channel system used to cover air conditioning line sets.