The major diameter of external threads is normally smaller than the major diameter of the internal threads, if the threads are designed to fit together. But this requirement alone does not guarantee that a bolt and a nut of the same pitch would fit together: the same requirement must separately be made for the minor and pitch diameters of the threads. Besides providing for a clearance between the "crest" of the bolt threads and the "root" of the nut threads, one must also ensure that the clearances are not so excessive as to cause the fasteners to fail.