This tensioning device was designed to go with any Adjustment Arm. It is available here by itself for mounting on your adjustment arm. It is designed to be used with out having to make any modifications to the arm, as shown below.
NOTE FROM THE PICTURE ABOVE: The adjustment mechanism takes up quite a bit of room at the end of the arm so if your arm is short it will reduce the amount of adjustment available. In that case you would be much better off getting the complete arm with adjustment mechanism. The complete unit is longer and even though the adjustment mechanism takes up some room at the end you get left with the same amount of adjustment you had before.