Full definition
The distance in millimeters (or inches) between two consecutive tooth centers on a timing belt, measured along the pitch line (the line at the center of the tension cord). This is the fundamental parameter defining timing belt and pulley compatibility — belt and pulley must have identical pitch. Common metric HTD pitches: 3M (3 mm, light duty), 5M (5 mm, general purpose), 8M (8 mm, medium-heavy), 14M (14 mm, heavy industrial), 20M (20 mm, extreme). Imperial pitches: MXL (0.080"), XL (0.200"), L (0.375"), H (0.500"), XH (0.875"), XXH (1.250"). Per ISO 5296 and ISO 13050. Smaller pitch = finer teeth, smoother motion, lower load capacity. Larger pitch = coarser teeth, higher load capacity, more vibration. The pitch line diameter of the pulley (not the OD) determines the actual drive ratio.