A thermal anemometer or mass flow meter typically having temperature and flow velocity sensor elements is provided in which a thin film temperature sensor is used in the heated sensor of the fluid velocity sensor element of the system. At least one thin-film RTD sensor is held within a spacer or interface member and the spacer, optionally, received within a housing. The thermal anemometer is preferably constructed to offer sufficient precision and accuracy in its design to be suitable for sensitive scientific and industrial applications. This goal is achieved while using cost effective parts by employing a construction approach in which the spacer and RTD sensor(s) is secured in place by solder, braze or another compound flowed into place while inserting the spacer and/or sensor(s).