Aid for running dogs safely with bike/kickbike/kicksled. The spring keeps running leash from tangling into wheel in case that the dog suddenly slows down. The spring smoothes all sudden movements too. Note. The model's name has changed from Race to Universal in 2017. includes two different U-bolt attachments (38mm and 54mm diameter) spring can be easily removed when adapter is not needed weight 390g, length 52cm Additional Kainpo Nylon Attachment Ring is sold separately If you you want to run the dog also beside the bike, we recommend choosing the Kainpo Bikejoring Adapter Combi PLUS.