A retractable helicopter landing gear has a suspension structure supporting one wheel, and is movable between a withdrawn position, to reduce drag on the helicopter, and a lowered position for landing and takeoff of the helicopter. The plate body is configured and adapted to be affixed between end flanges of adjacent pipes in a coal piping system so as to generally align the central orifice with an internal flow passage through the coal piping system. The first core portion is positioned adjacent the shaft to define a first space. The improved insulative properties of the nozzle construction in turn facilitates the use of higher strength, longer wear materials for the tundish nozzle. The state of overlap of the defect is determined as within the pattern, over the pattern, or outside the pattern, and the defect is automatically classified.