Abstract: A novel transducer useful in monitoring dynamic variations in the diameter of a fuel injector pipe is disclosed. A transducer body envelopes a portion of the diesel pipe by virtue of an elongate passageway therethrough. The body is secured to the pipe at either of its ends, and intermediate its ends, is characterized by a thin and planar transverse bridge section which lies in a plane parallel to the axis of the passageway. One or more strain detecting elements are mounted on the exterior of the bridge. The interior surface of the bridge may be spaced a finite distance from the pipe and bonded thereto by a bead of epoxy or the like. The transverse side of the bridge may also be separated from the remainder of the transducer body by means of two spaced apart holes or slots.