Picking the right timing belt starts with four numbers: torque, speed, centre distance, and the environment. Work through each one and the right profile almost picks itself.
For light office-machine drives under 1 kW and below 1000 rpm, a trapezoidal XL or T-profile PU belt is enough. Above that, an HTD or RPP profile is the safer choice — they share load across a curved tooth instead of a single contact line.
Material matters more than people expect: PU wins on cleanliness, chemical resistance, and precision; rubber wins on shock load and cost. If the drive is in a clean room or near food, PU is the default; if it is on a packaging line or a machine tool, rubber is the default.