An intravascular device delivery system , the system comprising: an elongated member , the elongated member including: a steerable catheter having a proximal end, a distal end, and a longitudinal axis extending therebetween; and a flexible hypotube positioned radially outside and circumferentially about the steerable catheter and coaxial with the steerable catheter , the flexible hypotube including at least one island cut and at least one slit cut to direct flexibility of the flexible hypotube , wherein the flexible hypotube and the steerable catheter are rotationally fixed to one another at a first key assembly , a first tab engaging with a first slot to form the first key assembly , and the first slot having a first slot length configured to at least partially determine an amount of longitudinal displacement of the steerable catheter relative to the flexible hypotube as the steerable catheter extends distally beyond a distal end of the flexible hypotube as the first tab moves longitudinally within the first slot , characterised in that the steerable catheter has a body , the body including a lumen contained within a wall of the body that extends along a least a portion of a longitudinal length of the steerable catheter , and one or more cuts made in an outer surface of the body through to the lumen , the first tab being inserted into the one or more cuts , and the cuts being configured to retain the first tab in the body of the steerable catheter with at least a portion of the first tab extending radially from the body . an elongated member , the elongated member including: a steerable catheter having a proximal end, a distal end, and a longitudinal axis extending therebetween; and a flexible hypotube positioned radially outside and circumferentially about the steerable catheter and coaxial with the steerable catheter , the flexible hypotube including at least one island cut and at least one slit cut to direct flexibility of the flexible hypotube , a steerable catheter having a proximal end, a distal end, and a longitudinal axis extending therebetween; and a flexible hypotube positioned radially outside and circumferentially about the steerable catheter and coaxial with the steerable catheter , the flexible hypotube including at least one island cut and at least one slit cut to direct flexibility of the flexible hypotube , wherein the flexible hypotube and the steerable catheter are rotationally fixed to one another at a first key assembly , a first tab engaging with a first slot to form the first key assembly , and the first slot having a first slot length configured to at least partially determine an amount of longitudinal displacement of the steerable catheter relative to the flexible hypotube as the steerable catheter extends distally beyond a distal end of the flexible hypotube as the first tab moves longitudinally within the first slot , characterised in that the steerable catheter has a body , the body including a lumen contained within a wall of the body that extends along a least a portion of a longitudinal length of the steerable catheter , and one or more cuts made in an outer surface of the body through to the lumen , the first tab being inserted into the one or more cuts , and the cuts being configured to retain the first tab in the body of the steerable catheter with at least a portion of the first tab extending radially from the body . <EOS>