A connector system comprising: an interface connector having: a housing having a main body holding a contact array therein, the housing extending between a front end and a back end along a mating axis, the interface connector including a cavity therein open to the front end and open to the back end, the cavity situated proximate to a side of the housing, the cavity having a receiving channel open to the side of the housing, the interface connector having mounting shoulders (144, 170) at least partially extending therein; and a fastener having a retention surface, the fastener configured to be side-loaded into the receiving channel, the mounting shoulders (144, 170) engaging the fastener to secure the fastener within the cavity to limit transaxial movement of the fastener along the mating axis, the connector system further comprising a receptacle connector including a complementary threaded receiver held by a receptacle housing, characterised in that: (i) the housing includes the cavity; (ii) the receiving channel has the mounting shoulders (144, 170) at least partially extending therein; (iii) the fastener is configured to be side-loaded into the receiving channel through the side of the housing; and (iv) the mounting shoulders (144, 170) further comprise upper mounting shoulders (144a, 144b, 144c, 144d) extending into the receiving channel, the upper mounting shoulders (144a, 144b, 144c, 144d) engaging a contact surface of the fastener to limit movement of the fastener axially along the mating axis; (v) the mounting shoulders (144, 170) further comprise lower mounting shoulders (170a, 170b, 170c) axially offset relative to the upper mounting shoulders (144a, 144b, 144c, 144d) such that the upper and lower mounting shoulders are staggered along the mating axis and receive a portion of the fastener therebetween; (vi) the fastener includes a head having a drive portion, the lower mounting shoulders (170a, 170b, 170c) extending radially inward in the receiving channel such that the lower mounting shoulders (170a, 170b, 170c) provide alignment of a mating tool to the drive portion of the head. an interface connector having: a housing having a main body holding a contact array therein, the housing extending between a front end and a back end along a mating axis, the interface connector including a cavity therein open to the front end and open to the back end, the cavity situated proximate to a side of the housing, the cavity having a receiving channel open to the side of the housing, the interface connector having mounting shoulders (144, 170) at least partially extending therein; and a fastener having a retention surface, the fastener configured to be side-loaded into the receiving channel, the mounting shoulders (144, 170) engaging the fastener to secure the fastener within the cavity to limit transaxial movement of the fastener along the mating axis, a housing having a main body holding a contact array therein, the housing extending between a front end and a back end along a mating axis, the interface connector including a cavity therein open to the front end and open to the back end, the cavity situated proximate to a side of the housing, the cavity having a receiving channel open to the side of the housing, the interface connector having mounting shoulders (144, 170) at least partially extending therein; and a fastener having a retention surface, the fastener configured to be side-loaded into the receiving channel, the mounting shoulders (144, 170) engaging the fastener to secure the fastener within the cavity to limit transaxial movement of the fastener along the mating axis, the connector system further comprising a receptacle connector including a complementary threaded receiver held by a receptacle housing, (i) the housing includes the cavity; (ii) the receiving channel has the mounting shoulders (144, 170) at least partially extending therein; (iii) the fastener is configured to be side-loaded into the receiving channel through the side of the housing; and (iv) the mounting shoulders (144, 170) further comprise upper mounting shoulders (144a, 144b, 144c, 144d) extending into the receiving channel, the upper mounting shoulders (144a, 144b, 144c, 144d) engaging a contact surface of the fastener to limit movement of the fastener axially along the mating axis; (v) the mounting shoulders (144, 170) further comprise lower mounting shoulders (170a, 170b, 170c) axially offset relative to the upper mounting shoulders (144a, 144b, 144c, 144d) such that the upper and lower mounting shoulders are staggered along the mating axis and receive a portion of the fastener therebetween; (vi) the fastener includes a head having a drive portion, the lower mounting shoulders (170a, 170b, 170c) extending radially inward in the receiving channel such that the lower mounting shoulders (170a, 170b, 170c) provide alignment of a mating tool to the drive portion of the head.