31” Modern micro-groove belt for flat pulleys.

This can be one of the most bedeviling questions concerning the Model T. Over the years and by the hands of many owners, the parts may have been changed on the engine and in not a few cases the engine itself has been changed out for one of a year different than that of the car in question. All of these variables can make it imprecise to order a belt by the "year" of the car.

The fool proof way to order a belt is really simple:

• First, adjust the fan to it's lowest position.
• Second, run a piece of string around the pulleys.
• Third, measure the string. This is the length needed for your belt.
• Do not measure with a steel tape, it won't bend tight enough around the pulleys and will give a false measurement. Also do not measure around the outside of an old belt, you will get a reading longer than you need.