NOTE: It is vital to use the same size and depth of nut as originally fitted to your hang glider.
Using the wrong nut courts disaster. So check the nut you remove carefully and make certain that you order the same size and thickness replacement.
The quarter inch UNF THIN is quite a popular nut size on many hang gliders. (However this thin nut can be difficult to source.)
If you removed a thin nut then replace with another thin. In this way the Nylon locking mechanism will work correctly. Using a thick nut could be dangerous as the bolt threads might not engage the Nylon and thus the nut would be more likely to come undone.