[en] Mensuration of the bores of boiler feed control ferrules in-situ within the AGR boilers can be done using a Central Electricity Research Laboratories-designed probe and ancillary equipment. From these measurements it is possible to determine the loss coefficients of the ferrules with fair accuracy. These loss coefficients may differ from the intended values because of poor quality control during manufacture or because of erosion and oxide deposition in service. This Report describes the construction and operation of the equipment. (author)