The rules of tennis specify that the height of the net should be 36 inches in the center. But the rules also specify that the height of the net above the singles sidelines should be 42 inches. Because the preponderance of courts in the world are designed and built to accommodate singles and doubles play, the net post is installed just outside the doubles sidelines—and so the 42-inch height is above the doubles sidelines.
So, on most courts, the net is too low above the singles sidelines. Singles sticks are 42-inches high and they prop-up the net above the singles sidelines perfectly.
When positioned correctly, the singles sticks give the net a pronounced “V” shaped slope.