An occlusive medical device system may include an elongate shaft having a distal strain relief portion and a lumen extending longitudinally through the elongate shaft, the elongate shaft including a plurality of retaining arms extending distally from the distal strain relief portion； an occlusive medical device including a proximal mounting portion fixed to an expandable occlusive element； and a release wire disposed within the lumen of the elongate shaft. The plurality of retaining arms may extend into the proximal mounting portion. The release wire may be configured to engage the plurality of retaining arms in a distal engagement position, thereby urging the plurality of retaining arms radially outward into releasable engagement with the proximal mounting portion. When the release wire is in a proximal released position, the plurality of retaining arms is deflectable radially inward to disengage from the proximal mounting portion.
