A catheter system, comprising: a catheter adapter, comprising a proximal end, a distal end, and a lumen extending therebetween, wherein the proximal end comprises a first slot, a second slot, and a proximal lumen opening, the lumen comprises a septum, the distal end comprises a catheter configured to be inserted into vasculature of a patient, and the catheter adapter is configured to be selectively coupled with a distal end of a needle shield; and an extension, comprising a distal end, a proximal end, and a lumen extending therebetween, the distal end comprising: a first cantilever arm having a distal end comprising a hook; a second cantilever arm having a distal end comprising a hook; and an insertion feature positioned between and spaced apart from the first and second cantilever arms, wherein the insertion feature is configured to insert into the proximal lumen opening of the catheter adapter to open the septum and provide a fluid connection between the catheter adapter and the extension, and wherein the first cantilever arm and the second cantilever arm are configured to insert within the first and second slots, respectively, whereby the distal ends of each of the first and second cantilever arms deflect outwardly as the hook of the corresponding cantilever arm is inserted into the corresponding slot, and, upon further insertion, the hook of the distal end of each of the first and second cantilever arms reaches and engages a groove in a snap-fit connection, whereby the first and second cantilever arms return to an original shape. a catheter adapter, comprising a proximal end, a distal end, and a lumen extending therebetween, wherein the proximal end comprises a first slot, a second slot, and a proximal lumen opening, the lumen comprises a septum, the distal end comprises a catheter configured to be inserted into vasculature of a patient, and the catheter adapter is configured to be selectively coupled with a distal end of a needle shield; and an extension, comprising a distal end, a proximal end, and a lumen extending therebetween, the distal end comprising: a first cantilever arm having a distal end comprising a hook; a second cantilever arm having a distal end comprising a hook; and an insertion feature positioned between and spaced apart from the first and second cantilever arms, a first cantilever arm having a distal end comprising a hook; a second cantilever arm having a distal end comprising a hook; and an insertion feature positioned between and spaced apart from the first and second cantilever arms, wherein the insertion feature is configured to insert into the proximal lumen opening of the catheter adapter to open the septum and provide a fluid connection between the catheter adapter and the extension, and wherein the first cantilever arm and the second cantilever arm are configured to insert within the first and second slots, respectively, whereby the distal ends of each of the first and second cantilever arms deflect outwardly as the hook of the corresponding cantilever arm is inserted into the corresponding slot, and, upon further insertion, the hook of the distal end of each of the first and second cantilever arms reaches and engages a groove in a snap-fit connection, whereby the first and second cantilever arms return to an original shape.