In order to estimate how far out (measured from the center of the boom) a quad wire of a given length will intersect with a spreader, use this formula:

Take the total wire length of the quad loop in feet (for example, 70.79 ft for a driven element on the 20 meter band) and divide it by 4....(about 17.7 in our example). Then square the result...(about 313.3 in our example). Divide this figure by 2....(about 156.65 for the example) and then take the square root. For our example, this yields the result 12.51, so you know that the wire intersect point will be 12.51 feet out the spreader, measured from the center of the boom.