The commonly used size of agricultural water belts, also known as layflat hoses or discharge hoses, can vary depending on the specific application and region. However, some commonly available sizes for agricultural water belts range from 2 inches (50 mm) to 6 inches (150 mm) in diameter.

These water belts are typically used for irrigation purposes, where they are unrolled and laid flat to deliver water to crops. The size selection depends on factors such as the desired flow rate, pressure requirements, and the size of the irrigated area.

It's important to note that availability and specific size options may vary based on local suppliers, manufacturers, and regional preferences. Therefore, it's always recommended to consult local agricultural equipment suppliers or manufacturers to determine the commonly used sizes for agricultural water belts in your specific area.