By using Federal Express, I was able to keep track of the arrival times.  On the top there are tiny holes drill in a pattern on both sides.  On the left there are 12 holes about 12 inches in and about 5 inches from the front.  On the right side there are 17 holes about 12 inches in and about 10 inches from the front.  The holes are drilled in a pattern about 1/2 inch wide by 3 inches.  One of the knobs was defective as the screw only went in about 1/8 of an inch not enough to tighten the knob.