[quote name='iconic' timestamp='1386353863' post='2299268']
Ive a jack that i love and never seems to goes out of tune.
I'm interested in what causes the slipping issue?
[/quote]
The threaded portion of the tuner knob is steel and the slider/string retainer is aluminium, so a lot softer. The thread in the slider can just strip, especially if you don't keep them well lubricated. I've fixed this on a couple of Jack Basses by drilling and tapping out the slider to take an M4 Helicoil, a steel threaded insert. There is just enough meat on the slider to do this, and it only takes about 5 minutes if you have the Helicoil kit.