I took them off with an impact wrench..but i cant get them back on..the strut shaft just spins and there is nothing to hold on to......

how can I screw the top bolt down tight?

 

Use a box end on the nut and use a crescent to hold the center...

 

yeah that would work but its a lock nut that goes on and when I start the nut it gets real tight and covers the flat part of the center/top of the screw shaft and that leaves nothing to grab on to.....I figured an impact would ru the bolt right on down but it doesnt...