So my passenger-side fender is rusted really bad just behind the headlamp assembly. Fortunately, I lucked out at the junkyard & found one in great shape. Removing it was not a problem - until I got to the last bolt. That last bolt was located at the lower left of the fender. It would not loosen, just spin and spin. It seems like a captive nut (?) holding that section of the fender in place broke free. After losing my patience ( and with the junkyard soon closing ) I just pulled it loose. The damage I caused is fixable.
Upon checking this same bolt on my truck, it too just spins w/o loosening.

If anyone knows a trick to loosen this bolt, or if it is designed this way, I will surely appreciate any help.

Thanks.

 

No trick that I know of... If you can get vice grips in behind to hold the nut and then turn the bolt out. I've never removed a fender but did have to fix my headlight assm bolts. Same problem, the bolt just spun and spun, ended up drilling out the whole bolt and nut assm and used new bolts with nylocs in behind.