An axle connector adapter assembly, including: a frame element with a first frame member; an axle extending along an axial axis and including an engagement end with a first threadable portion; and an adapter with a second threaded portion for threadable engagement with the first threadable portion. The first frame member includes an open slot with an open entrance portion, a closed terminus region, slot sidewalls extending between the open entrance portion and the closed terminus region, a slot axis, an axially outward facing first outboard face, and an axially inward facing first inboard face. The adapter is assembled to the first frame member to include a rotationally keyed engagement between the adapter and the first frame member to limit rotation of the threaded portion relative to the first frame member about the axial axis. The adapter is preferably axially retained to the first frame member.