Masonry Opening Width
The MO width is the measurement of the opening from left masonry to right masonry. When determining the Masonry Opening, there is a 1/4″ adder to each piece of brickmould to account for the backer rod that is used.
Masonry Opening Height
The MO height is the measurement of the opening from the header masonry to subfloor. When determining the Masonry Opening, there is a 1/4″ adder to each piece of brickmould to account for the backer rod that is used.
The unit sits in the Masonry Opening. Therefore the Brickmould Dimension and the Masonry Opening are related. If you are able to determine one, you are able to determine the other.