Abstract: A sensor for magnetic-inductive flowmeters in defined by a sensing tube (3) disposed in a steel housing (1) and fitted with sensing electrodes (5). Two opposing magnetic coils (6) are mounted to the exterior of the tube. The coils (6) have a bolt-shaped core (7) which have saddle-shaped bases that engage the outer wall of sensing tube (3). A simplified mounting of magnetic coils (6) in steel housing (1) is achieved with flange-like webs (12) mounted adjacent an upper end (11) of coil core (7). The webs are positioned within steel housing (1) by support surfaces (29). A winding bobbin (14) is constructed of two semi-cylindrical halves (15,16) which are disposed about coil core (7) and are locked to each other with a spring catch (22). The coil wire (17) is wound about the bobbin (14) secured to core (7).