Full thread bolts have no thread-free portion, meaning that the threads run from under the head to the tip. The fully threaded bolts are normally usually used in situations where grip strength is very critical. The fact that the entire shaft is threaded means that all the tension placed on the bolt is spread over the entire structure, and this means that it can withstand greater forces than the partially threaded ones. One of the major advantages of fully threaded bolts is that they rarely shear, and tend to not loosen as much.