A fluid flow velocity measuring device is shown. In the preferred and illustrated embodiment, an elongate body receives a removable spinner cartridge assembly. The assembly is formed of an elongate sleeve surrounding a rotating shaft supported by bearing assemblies at opposite ends of the shaft. The shaft supports a spinner. Particular sizes of spinners are calibrated to a particular flow velocity ranges and density of material. The insert is held in position by a compressed spring behind the insert so that fluid flow is directed from an inlet port in the tool adjacent a petal basket, along an axial passage in the tool, and through the spinner and out through an outlet port.