Each vertical member should have two holes 180 degrees apart at each end, in line with the horizontal members as indicated by the arrows. Vertical members' hole placement should be as shown in A and B. Preferably, the size of the holes should be equal, and thetwo holes' combined area should be at least 30% of the cross-sectional area at either end of the verticals (Areas C and D or Areas E and F).

Horizontal End-Plates

1. Completely open with the same hole diameter as the internal diameter of the tube is most desirable.
2. Equal substitutes would have openings at least 30% of the area of the internal diameter as shown.