I have a 96' LEgacy L Sedan AWD with a cable clutch.....the lock nut was lost by the previous owner. Now whenever i press on the clutch pedel the adjusting nut comes loose...I was just wondering the thread size of the clutch cable....if anyone knows it would be very helpful (it seems every size i try doesnt fit).

6 X 1.25.

They're all metric, that might be the key if you were trying standard sizes. It is good to know that most of the threads on Subaru's are a 1.25 pitch thread, very simple, just need to find the diameter. Easiest solution would have been to take the other adjusting nut into Lowes with you and match it up on their thread finder charts.