Install special hook provided into center hole of the insert and maneuver it into cut-out block.
After the insert is lined up, pull and twist hook in all directions to tighten flanges on inside of insert to the block.
Insert should be about 1/4" x 3/8" recessed at finished position. Patent #D375574
Made for 3 1/2" cut-out block.
Heckmann Building Products