Abstract: An extrusion calibrator, to calibrate the exterior profile of a thermoplastic extruded product exiting from an extrusion die, has a modular calibrating cassette of calibrating plates in a surrounding shell. One calibrating cassette is readily interchangeable within the shell for another calibrating cassette of a different extruded product cross-sectional profile. The cassette plates have planar surfaces, free of fluid-conducting pathways, which greatly reduces the time, cost and skill required to establish vacuum and coolant conducting routes through the extrusion calibrator. Fluid conducting routes to conduct vacuum and coolant through the calibrator are established by vacuum and coolant conducting manifolds and channels in the shell interior and by interplate spacings mating with these channels.