FIELD: medicine.SUBSTANCE: group of inventions relates to medical equipment, namely, to a medical device for use in the vessel of a patient for the purpose of diagnosing or treating the patient, such as mapping tissue and/or ablating tissue using radio frequency or other sources of energy, and more particularly, to a deflectable catheter having a flat beam for on-plane bi-directional deflection. Catheter comprises an elongated catheter body, a deflectable section, a control handle, a flat beam, at least one fiber puller member and ferrule. Elongated catheter body comprises a first tubular structure having a first central lumen, a distal end and a proximal end. Deflectable section has a second tubular structure having a second central lumen, and a proximal end that is distal of the proximal end of the catheter body. Control handle is proximal of the catheter body. Flat beam has first and second opposing surfaces. Flat beam extends through at least the second central lumen of the deflectable section. At least one fiber puller member extends from the catheter body and through the deflectable section. At least one fiber puller member has a distal end. Ferrule anchors the distal end of the at least one fiber puller member to the first surface of the beam. Ferrule has a lumen, an outer underside, a thin planar distal portion and a weld formation between the thin planar distal portion and the first surface of the beam. Distal end of the at least one fiber puller member extends into the lumen only through a proximal portion of the ferrule. Flat outer underside abuts against the first surface of the beam. Thin planar distal portion devoid of the fiber puller member. According to a second embodiment, the catheter comprises a first and a second fiber puller members extending from the catheter body through the deflectable section, each puller member has a respective distal end and a first and second ferrule, fixing the distal end of the respective fiber puller member to the fir
