Abstract: An improved clamp-on arrangement having a first sensor assembly (2, 2′) and a second sensor assembly (3, 3′) usable for different nominal diameters of pipes. The sensor assemblies can be positioned either along a single straight surface line (11) or along diametrically opposed straight surface lines (11′, 11″) of the pipe. The arrangement contains replaceable components, so that in the event of a malfunction, only faulty components need to be replaced. The assemblies (2, 2′; 3, 3′) are attached by means of pipe straps (4, 4′); (5, 5′) and wherein the assemblies are identical in construction. Each assembly has a flat bracket (6) adjacent to the pipe and having a longitudinal center line (61) and a tubular portion (62) integrally formed thereon. A sensor inset (63) is longitudinally guided in the tubular portion (62) and contains an ultrasonic transducer (64) with a transducer element (644).