The smallest three-point hitch is a category 0 and has 5/8-inch diameter upper and lower link holes and a 20-inch separation between lower link holes. It's designed for use on a 20-horsepower tractor. Three-point hitches sizes have five categories as defined by the International Standards Organization ISO 730 standard.
Category 4 is the largest three-point hitch size, and it has a 1 3/4-inch upper link hole and 2-inch lower link holes with a 46-inch separation, which is suitable for use on 180- to 400-horsepower tractors. Categories 3, 2 and 1 step down in link hole sizes and lower link spread and horsepower capacity accordingly. A three-point hitch consists of five main components, including the upper hitch point, the upper link arm, the lift arms, the lower link arms and the lower hitch points.