The figure shows the location of holes and clipped corners, which must be flush. Using the following formulas, the table shows typical sizes of holes.

Internal Gussets

• Space at minimum of 36” (91 cm)

Box Sections

• If H + W = 24” (61 cm) or larger, the area of the hole, plus clips, should equal 25% of the cross-sectional area of the box (Area = H x W).
• If H + W is between 16” and 24” (41-61 cm), the area of the hole, plus clips, should equal 30% of the cross-sectional area of the box.
• If H + W is between 8” and 16” (20-41 cm), the area of the hole, plus clips, should equal 40% of the cross-sectional area of the box.
• If H + W is less than 8” (20 cm), leave completely open, with no end-plate or internal gusset.

The table below is for square box-sections only. For rectangular sections, calculate the required area and check with the galvanizer for positioning of openings.