if you have an outside dog, or even put the dog out for a while, & you have a line, like clothes line, line ran from tree to tree ect... this attaches to the line and to his collar and he is able to run up and down giving your pet much more free range to roam and play , but still be chained up safely . asking $3.00 we paid $17 for it. if interested please text or call 785-432-0817. we only stopped using it because we moved and dont have a line or a place to run a line to use the runner, but our dog loved being on his runner great for exercise for him and more of free range and still locked/tied up while oitside playing