The standard pumps are exactly 3 inches in diameter. (though we have 4″ pumps as well) The minimum well casing diameter for these pumps is 3.5 inches. The pump is made up of 2 parts. Our most popular models use the super-efficient helical pumping mechanism that drives the water up the well. We also carry centrifugal pumps.Designed and built to the highest quality standards, customers count on Cat Pumps products to keep their equipment running. Every design detail of Cat Pumps products is optimized for long-life and reliable performance, making Cat Pumps the most trusted name in high-pressure pumps and systems.