A fluid flow rate sensor includes a detection circuit which generates a first signal corresponding to an output voltage of a bridge circuit, and a second signal corresponding to a fluid temperature. It has a vertical arm attached to a horizontal arm ending in an end cap. The method includes the steps of performing an assembling process, performing a disassembling process, and performing in a commonly-used processing facility mutually reversible steps between the assembling and disassembling process andor performing steps which are identical for the assembling and disassembling processes.