An ultrasonic flow meter for measuring the flow of a fluid through a pipeline, comprising: a spool piece including a throughbore and a plurality of transducer ports (165, 465) extending from the outer surface of the spool piece to the throughbore; a transducer assembly (200, 500, 700, 800) disposed in one of the transducer ports, wherein the transducer assembly has a central axis and comprises: a piezoelectric capsule (210, 510) having a first end proximal the throughbore of the spool piece and a second end distal the throughbore of the spool piece, wherein the piezoelectric capsule comprises a piezoelectric housing (251, 551) and a piezoelectric element (212, 512) disposed in the piezoelectric housing, wherein the piezoelectric housing extends from the first end of the piezoelectric capsule to the second end of the piezoelectric capsule and includes a first counterbore (213, 215, 231, 233) extending axially from the first end of the piezoelectric capsule, wherein the piezoelectric element is disposed in the first counterbore of the piezoelectric housing; and characterized by a transformer capsule (250, 550) coupled to the piezoelectric capsule, wherein the transformer capsule comprises a transformer housing and a transformer disposed within the transformer housing; an annular seal radially disposed between the transducer assembly and the spool piece and axially disposed between the transformer capsule and the throughbore of the spool piece, wherein the seal assembly is configured to restrict the flow of fluid through the transducer port between the throughbore of the spool piece and the transformer capsule. a spool piece including a throughbore and a plurality of transducer ports (165, 465) extending from the outer surface of the spool piece to the throughbore; a transducer assembly (200, 500, 700, 800) disposed in one of the transducer ports, wherein the transducer assembly has a central axis and comprises: a piezoelectric capsule (210, 510) having a first end proximal the throughbore of the spool piece and a second end distal the throughbore of the spool piece, wherein the piezoelectric capsule comprises a piezoelectric housing (251, 551) and a piezoelectric element (212, 512) disposed in the piezoelectric housing, wherein the piezoelectric housing extends from the first end of the piezoelectric capsule to the second end of the piezoelectric capsule and includes a first counterbore (213, 215, 231, 233) extending axially from the first end of the piezoelectric capsule, wherein the piezoelectric element is disposed in the first counterbore of the piezoelectric housing; and a piezoelectric capsule (210, 510) having a first end proximal the throughbore of the spool piece and a second end distal the throughbore of the spool piece, wherein the piezoelectric capsule comprises a piezoelectric housing (251, 551) and a piezoelectric element (212, 512) disposed in the piezoelectric housing, wherein the piezoelectric housing extends from the first end of the piezoelectric capsule to the second end of the piezoelectric capsule and includes a first counterbore (213, 215, 231, 233) extending axially from the first end of the piezoelectric capsule, wherein the piezoelectric element is disposed in the first counterbore of the piezoelectric housing; and characterized by a transformer capsule (250, 550) coupled to the piezoelectric capsule, wherein the transformer capsule comprises a transformer housing and a transformer disposed within the transformer housing; an annular seal radially disposed between the transducer assembly and the spool piece and axially disposed between the transformer capsule and the throughbore of the spool piece, wherein the seal assembly is configured to restrict the flow of fluid through the transducer port between the throughbore of the spool piece and the transformer capsule.