ABSTRACT
When the lead of a bolt thread is the same as the nominal lead, the thread will engage fully into a mating thread with near-perfect lead, such as in a GO thread gage. Each thread ridge will fit into its mating thread groove over the length of engagement. But when the bolt thread lead is significantly longer or shorter, the mating thread will contact only some of the thread ridges and the thread ridges will not be able to fully engage all the grooves. (See Figure
fiGURE 9 A bolt with a long lead thread that causes its functional diameter to be larger than its pitch diameter .. A short lead thread would have the same effect. For nut threads with lead variations, the functional diameter is smaller than the pitch diameter.
