1. A DEVICE ADAPTED TO BE INTERPOSED BETWEEN A TRACTOR AND AN AGRICULTURAL IMPLEMENT WHICH HAS AT LEAST ONE WHEEL IN CONTACT WITH THE GROUND AND HAS A DRAFT CONNECTION WITH SAID TRACTOR AND IS EFFECTIVE FOR PREVENTING THE TRACTOR FROM OVERTURNING BACKWARDS WHEN THE DRAFT FORCE BECOMES EXCESSIVE, SAID DEVICE COMPRISING TWO TELESCOPIC MEMBERS CONNECTED AT ADJACENT ENDS FOR LIMITED RELATIVE SLIDING MOVEMENT IN THE DIRECTION FOR SHORTENING SAID DEVICE BUT BEING CAPABLE OF SUBSTANTIALLY FREE RELATIVE SLIDING TO ELONGATE THE DEVICE, SAID CONNECTION PERMITTING SAID LIMITED RELATIVE SLIDING MOVEMENT IN THE DIRECTION FOR SHORTENING SAID DEVICE COMPRISING MEANS PERMITTING AN INITIAL FREE MOVEMENT IN SAID DIRECTION AND RESILIENT MEANS RESISTING FURTHER MOVEMENT IN SAID DIRECTION, MEANS AT THE OTHER END OF ONE OF SAID IMPLEMENT, AND MEANS AT PIVOTALLY CONNECTING IT TO SAID IMPLEMENT, AND MEANS AT THE OTHER END OF THE OTHER OF SAID MEMBERS FOR UNIVERSALLY PIVOTALLY CONNECTED IT TO SAID TRACTOR AT A LOCATION VERTICALLY ABOVE SAID DRAFT CONNECTION.