The Nissan Path

I just put new heavy duty coils from ARB on my 1999 pathfinder. Somehow both of the top bolts on the top of the strut were stripped and i noticed this from some knocking on the front right side. The nut wont tighten down any more. The struts are KYB gr-2's. do i need to put some heavier duty struts on? or do you think was just a mistake I made when I tightened the bolts?

Please need help!