Abstract: A dam-shaped throttling block for use in a pipe, for the measurement of the flow rates of fluids. The shapes of four successive flat surfaces on the throttling block angularly-displaced relative one another in the flow direction, together with an aperture in the one of the flat surfaces extending parallel to the pipe longitudinal axis, create reduction of a cross-sectional area in one step from one that is unthrottled to one that is throttled, extending for a limited distance in the pipe, and then expansion of the cross-sectional area in two steps from the throttled one back to the unthrottled one so to provide for accurate measurements and an improved lifetime. Flow rates of highly viscous fluids and fluids that contain solid particles can be measured. Other benefits include reduced head loss, wide measurement range and reduced installation space.