Touchpad used for training “heel”. You can purchase the 2 Quart size for dogs who are 35 pounds or less. You can purchase the 4 Quarts + 2 Quarts for larger dogs. We do not sell the 4 Quarts by itself, dogs who need the 4 Quarts will need the support of the 2 Quarts underneath the 4 Quarts for stability.