A tether assembly for a delivery tool that deploys an implantable medical device includes an elongate shaft and an attachment member coupled to a distal end of the shaft, wherein the attachment member includes an external thread and an end wall, the end wall extending orthogonally with respect to a direction of travel within a valley of the external thread to provide a hard stop for a threaded attachment bore of the medical device, when the bore is mated with the external thread. The tether assembly may extend within a lumen defined by an elongate tube of an inner assembly of the delivery tool, such that the attachment member thereof is located in proximity to a distal member of the inner assembly, the distal member being coupled to a distal end of the tube and forming a distal opening of the lumen.