Apparatus for performing nondestructive magnetically testing and inspection of elongate objects. The apparatus concentrically surrounds the elongate object to be tested and includes means for inducing a magnetic field in the elongate object and a partial ferrous return path for the magnetic ...http://www.google.ca/patents/US5828213?utm_source=gb-gplus-sharePatent US5828213 - Method and apparatus for magnetically sampling the uniformity of an elongate object 
