6. For installing a factory mulled unit, apply 90-degree bent structural brackets 1 1/8" from the mullion on both sides of all jamb and head jamb mullion joints. This applies to nail fin or structural bracket installation. See Figure 11. For sill mullion joints, slide flat sill structural brackets into sill T-slot and position one on either side of each mullion joint. If mulled assembly has nailing fin, remove the nailing fin at the sill prior to sliding brackets on. Cut sill nail fin at each mullion joint location and shorten the ends by 3"-3.5" near each mullion to allow for the brackets. Slide brackets and nail fin pieces into the sill T-slot. See Figure 12.