what is pitch diameter
10 most extreme places on Earth. Pitch diameter is a term used to take measurements of the diameter of a gear or a screw using pitch points. Pitch points on a gear could be found if a straight line were drawn up from two of the gear's teeth located side by side and the two lines were connected by a curve.itch diameter measurement is used to help people find the right screws for a certain job. Pitch diameter is particularly useful if you are in need of replacement screws. Putting the wrong ones in could cause problems, so it's important to match them up with the old ones.