Pitch.

The pitch of a perforation is defined as the distance between one perforation and the next. This distance is measured from the lowest side of the first perforation, to the lowest side of the next one, measured along the length of the film.

Today both KS and BH types of perforations are manufactured in two different pitches, called long pitch and short pitch. These two pitches are designed to obtain the best results in the printing of positives on continuous printers, in which the negative remains inside the drum and the positive, which is placed above, has to cover a greater circumference. Here we are talking of thousandths of a millimetre; the dimensions of the two pitches: Long Pitch 35mm film has a pitch of 4.750 mm and Short Pitch [sometimes called Standard pitch], 4.740 mm.
The perforation specification defines both pitch and perforation type, for example KS-4750 and BH-4740 Generally the long pitch is used for the positive films (with KS perforations) used for printing on fast rotary gates, while the short pitch is generally used for negative, duplicate and intermediate stock exposed by lens systems in intermittent gates [and are BH perforations].