Chapter 5, Section D
THE FOUL LINE AND FOUL LIGHTS
The foul line is the dividing line between the lane and the approach area and is also the dividing line between a legitimate delivery and a foul call. It is normally made of a colored fibre substance or plastic material and embedded in the lane surface.
The foul line must be at least 3/8 of an inch wide but no more than one (1) inch wide. Measurements for length of lane and approach are made from the approach side of the foul line. The foul line is included in the measurements for length of lane but not approach
The modern foul detecting devise is an electronic eye or photo electric cell or tube positioned and focused on the foul line. The device consists of two units positioned at the outside edge of each channel sending a beam of light from one unit to the other. The beam is usually the same width as the foul line and about two inches high. Any encroachment upon the foul line will break the beam and activate the foul light's bell or buzzer. It is completely automatic.