A prosthetic device comprising: an upper member comprising: a guiding feature , comprising a sloped guiding track and a notch ; and a lower member comprising: a conical terminating section formed at a proximal end of the lower member, wherein the conical terminating section is adapted to fit into a conical void defined in the upper member and comprises a first conical part which has a steeper angle than a second conical part relative to a common axis of the upper and lower members; a locking head which is coupled to a proximal end of the first conical part and is adapted to fit into a conical void defined in the upper member; and a self-aligning feature comprising a protrusion extending radially from a section of the lower member and extending perpendicular to the common axis of the upper and lower members, in which the protrusion prevents the lower member from mating at an incorrect rotational position to the upper member; wherein contact of the self-aligning feature with the sloped guiding track as the conical terminating section is fitted into the conical void causes the lower member to rotate until the self-aligning feature is seated within the notch. an upper member comprising: a guiding feature , comprising a sloped guiding track and a notch ; and a lower member comprising: a conical terminating section formed at a proximal end of the lower member, wherein the conical terminating section is adapted to fit into a conical void defined in the upper member and comprises a first conical part which has a steeper angle than a second conical part relative to a common axis of the upper and lower members; a locking head which is coupled to a proximal end of the first conical part and is adapted to fit into a conical void defined in the upper member; and a self-aligning feature comprising a protrusion extending radially from a section of the lower member and extending perpendicular to the common axis of the upper and lower members, in which the protrusion prevents the lower member from mating at an incorrect rotational position to the upper member; a guiding feature , comprising a sloped guiding track and a notch ; and a lower member comprising: a conical terminating section formed at a proximal end of the lower member, wherein the conical terminating section is adapted to fit into a conical void defined in the upper member and comprises a first conical part which has a steeper angle than a second conical part relative to a common axis of the upper and lower members; a locking head which is coupled to a proximal end of the first conical part and is adapted to fit into a conical void defined in the upper member; and a self-aligning feature comprising a protrusion extending radially from a section of the lower member and extending perpendicular to the common axis of the upper and lower members, in which the protrusion prevents the lower member from mating at an incorrect rotational position to the upper member; a conical terminating section formed at a proximal end of the lower member, wherein the conical terminating section is adapted to fit into a conical void defined in the upper member and comprises a first conical part which has a steeper angle than a second conical part relative to a common axis of the upper and lower members; a locking head which is coupled to a proximal end of the first conical part and is adapted to fit into a conical void defined in the upper member; and a self-aligning feature comprising a protrusion extending radially from a section of the lower member and extending perpendicular to the common axis of the upper and lower members, in which the protrusion prevents the lower member from mating at an incorrect rotational position to the upper member; wherein contact of the self-aligning feature with the sloped guiding track as the conical terminating section is fitted into the conical void causes the lower member to rotate until the self-aligning feature is seated within the notch. <EOS>