Each vertical member should have two holes 180 degrees apart at each end, in line with the horizontal members. Vertical members' hole placement should be as shown in A and B.  Preferably, the size of the holes should be equal, and the two holes' combined area should be at least 30% of the cross-sectional area at either end of the verticals.

Horizontal End Plates

1. Completely open is the most desirable. 
2. If H + W  > 24” (61 cm), the area of the hole, plus clips, should equal 25% of the tube area (Area = H x W).
   • If H + W is > 16” and < 24” (41-61 cm), the area of the hole, plus clips, should equal 30% of the tube area.
   • If H + W is > 8” and < 16” (20-41cm), the area of the hole, plus clips, should equal 40% of the tube area.
   • If H + W is < 8” (20 cm), the tube should be left open.