Pitch in springs is a completely different definition compared to just the word pitch. When talking about the pitch in springs, there’s a coil. With an active coil you have distance, the distance from one center to the other center is called the pitch.
To break it down, lets say you have a spring with 10 active coils. The From the bottom coil to the top coil the total height is ten inches. Each active coil is spread out 1 inch per coil. The pitch of this spring would then be considered one inch.
