Abstract: A method of assembling an electromagnetic flow sensor which includes a length of tubular material (referred to herein as a “spool”) (1) intended to be fitted with a tubular insert (2) that is anchored relative to the spool once the spool is fitted into the pipeline. Sealing is preferably achieved by means of extensions of the insert material (typically elastomer) intended to be trapped between end fittings of the spool and abutting ends of the pipeline and secured when the spool is connected in fluid-tight manner to the pipeline. The insert is preferably reinforced against deformation under the application of pressure, and this can be achieved by incorporating one or more bands (4) of suitable material into the insert.