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 ideal for larger line set sizes, such as: 3/8 LL 5/8 SL, 3/8 LL 3/4 SL, or 3/8 LL 7/8 SL.

Features:

Wall Sleeve 3" x 9.4" – 7-3/4"
Used to provide a seal when penetrating walls. OD – 3"  ID – 2-7/8"