Pro's Pro Crank Tensioning Spring suitable for any Pro's Pro tennis crank tension mechanism stringing machine (Pilot or XP Plus). When uncompressed and not placed in the mechanism, the length is seven centimeters.
This spring is usually replaced when the actual tension is incorrect and calibration has also been attempted. Operating procedure with crank tension mechanisms is to reduce the tension to zero when not using the stringing machine. The likely reason for requiring a replacement spring is that the tension has not been reduced to zero, which results in spring rigidity changing / weakening.