Ultrasonic flowmeter for measuring the flow of a medium flowing through a measuring tube based on the travel time difference principle comprising: A measuring tube with a measuring tube wall for guiding said medium and at least one pair of housings extending to an outer side of said measuring tube wall; at least one pair of ultrasonic transducers each with a transducing element for generating and/or sensing ultrasonic pulses and a transducer body containing said transducing element, wherein said ultrasonic pulses travel between said transducers along a path, wherein at least one subpath of a path extending between said pair of transducers is non-parallel to a measuring tube axis of said measuring tube; an electronic circuit for operating said ultrasonic transducers and for evaluating of sensed ultrasonic pulses; wherein each of said housings is arranged to house one of said transducers, and wherein said housings comprise an inner surface and a first longitudinal axis and an inner first diameter orthogonal to said first longitudinal axis; wherein said transducer comprises a circumferential surface, and wherein said transducer body comprises a second longitudinal axis, and wherein said transducer comprises an end face exposable to said medium, wherein said end face is set for transferring said ultrasonic pulses between said transducing element and said medium and vice versa, and wherein a first sector of said transducer comprising said end face of said transducer body has a maximum second diameter orthogonal to said second longitudinal axis, and wherein said housing encompasses said circumferential surface at least partially, characterized in that said transducer comprises at least one first protrusion protruding from said circumferential surface into a gap between said transducer body and said housing, wherein a height of the first protrusion is smaller than the width of said gap and/or that said housing comprises at least one second protrusion protruding into said gap, wherein a height of the second protrusion is smaller than the width of said gap. A measuring tube with a measuring tube wall for guiding said medium and at least one pair of housings extending to an outer side of said measuring tube wall; at least one pair of ultrasonic transducers each with a transducing element for generating and/or sensing ultrasonic pulses and a transducer body containing said transducing element, wherein said ultrasonic pulses travel between said transducers along a path, wherein at least one subpath of a path extending between said pair of transducers is non-parallel to a measuring tube axis of said measuring tube; an electronic circuit for operating said ultrasonic transducers and for evaluating of sensed ultrasonic pulses; wherein each of said housings is arranged to house one of said transducers, and wherein said housings comprise an inner surface and a first longitudinal axis and an inner first diameter orthogonal to said first longitudinal axis; wherein said transducer comprises a circumferential surface, and wherein said transducer body comprises a second longitudinal axis, and wherein said transducer comprises an end face exposable to said medium, wherein said end face is set for transferring said ultrasonic pulses between said transducing element and said medium and vice versa, and wherein a first sector of said transducer comprising said end face of said transducer body has a maximum second diameter orthogonal to said second longitudinal axis, and wherein said housing encompasses said circumferential surface at least partially, characterized in that said transducer comprises at least one first protrusion protruding from said circumferential surface into a gap between said transducer body and said housing, wherein a height of the first protrusion is smaller than the width of said gap and/or that said housing comprises at least one second protrusion protruding into said gap, wherein a height of the second protrusion is smaller than the width of said gap.