Abstract: A probe holder for a rotary scanner, the probe holder having a shaft and a plate rotatably mounted to the shaft. A parallelogram arrangement comprising a probe support on one side for holding a probe, an annular counterweight on an opposite side and a pair of levers therebetween secured to the plate. A spring mechanism in the annular counterweight moves the probe radially inwardly into contact with a pipe to be measured. A pair of spring-biased arms for contacting the pipe and centering the probe on the pipe are mounted to one end of the plate. A second counterweight is secured to the other end of the plate to counterbalance the contact arms.