Our Lower Flex Extension adds extra protection for your horse and is designed to flex in all directions adding no hindrance to the movement of your horse and still give it that extra protection. The 1/2 Knee Extension offers protection for the horse that hits high between the tendon boot and knee boot. This 1/2 knee extension fits excellently under our Protecto knee boot which gives you complete protection. You say you don't need the 1/2 knee, then simply trim off what you don't need, customizing our boot to your horse. If you trim off the 1/2 knee and lower extension you have the basic standard tendon boot. This boot comes in two sizes--X-S-Small and Med-X-Large.