in manner above discussed transducer 100 is shown in disposition examining the exterior surface of test object 112 with the portion of winding 110 spanning opening 104 confronting the test object periphery through an air gap as is seen in this embodiment although the transducer has a smaller diameter than the test object selection of the geometry of opening 104 and the locations of the radially outward ends of sidewalls 106 and 108 enable winding 110 to be in surface conformity with the object perimeter thus winding 110 can be viewed as having successive courses at different radii the course spanning opening 104 having the test object radius and the course upon the surface of conductive member having the radius thereof a like diverse radii transducer 200 is seen in fig1 with a convex winding course in testing relation to the interior wall 202 of a test object in this instance insert 204 is retained with the transducer assembly in use thereof serving to maintain surface conformity of the winding with the test object in this case the insert is selected to be of electrically nonconductive material whereas its composition is not of consequence in the application of fig1 8 or the application of fig9 since the insert is removed from the transducer in adapting same for use the above discussed characteristic of known monoturn transducers wherein flux density is increased upon aperture size reduction applies likewise in the transducers of the invention wherein the opening such as 104 of fig9 corresponds to the combined slot and central aperture of the known monoturn for this purpose in this context lessening the size of opening 104 from that shown in fig9 will increase flux density issuing from the transducer inductance likewise is more a function.