Abstract: The testing of glass containers for structural defects, principally in the side wall surfaces thereof, is provided wherein bottles are conveyed in succession at spaced-apart intervals through the testing device. The testing device takes the form of a wheel having a substantial thickness mounted to rotate about a vertical axis, with the periphery of the wheel extending over a portion of the width of the conveyor belt. A pressure plate having a vertical surface facing in the direction of the wheel and positioned and supported from the opposite side of the conveyor has a surface configuration closely paralleling that of the curvature of the wheel. The pressure plate and wheel are positioned relative to each other such that a container, in order to pass between the wheel and the pressure plate, is subjected to a lateral compressive force. Because of the contour of the wheel and length of the pressure plate, at least 180.degree.