A prosthetic attachment system comprising: an insert arranged for connection to a closed distal end of a prosthetic liner; an attachment unit arranged for connection to a distal end of a prosthetic socket, the attachment unit comprising a body defining an axis and a central opening for selectively receiving the insert; a plurality of locking elements carried by the body, the plurality of locking elements being circumferentially distributed about the axis and radially repositionable relative to the axis; and a release mechanism slidably repositionable on an outer surface of the body to move the prosthetic attachment system between a locked configuration in which the plurality of locking elements are radially repositioned to lock the insert in the central opening and an unlocked configuration in which the insert is released from the central opening; wherein the body includes a support body, a lock body carrying the plurality of locking elements and defining the central opening, and a stop member in the central opening, and at least one resilient member arranged to bias the stop member upwardly within the central opening, wherein the at least one resilient member comprises a plurality of spring members circumferentially distributed about the axis, the plurality of spring members collectively bias the stop member away from the bottom of the support body, the lock body includes an annular flange surrounding the central opening and extending axially upward and radially away from a top of the central opening, the annular flange arranged to funnel the insert into the central opening, and a top surface of the release mechanism defines a shoulder corresponding to a bottom of the annular flange on the lock body such that relative axial movement between the release mechanism and the lock body is limited by engagement of the shoulder with the bottom of the annular flange. an insert arranged for connection to a closed distal end of a prosthetic liner; an attachment unit arranged for connection to a distal end of a prosthetic socket, the attachment unit comprising a body defining an axis and a central opening for selectively receiving the insert; a plurality of locking elements carried by the body, the plurality of locking elements being circumferentially distributed about the axis and radially repositionable relative to the axis; and a release mechanism slidably repositionable on an outer surface of the body to move the prosthetic attachment system between a locked configuration in which the plurality of locking elements are radially repositioned to lock the insert in the central opening and an unlocked configuration in which the insert is released from the central opening; wherein the body includes a support body, a lock body carrying the plurality of locking elements and defining the central opening, and a stop member in the central opening, and at least one resilient member arranged to bias the stop member upwardly within the central opening, wherein the at least one resilient member comprises a plurality of spring members circumferentially distributed about the axis, the plurality of spring members collectively bias the stop member away from the bottom of the support body, the lock body includes an annular flange surrounding the central opening and extending axially upward and radially away from a top of the central opening, the annular flange arranged to funnel the insert into the central opening, and a top surface of the release mechanism defines a shoulder corresponding to a bottom of the annular flange on the lock body such that relative axial movement between the release mechanism and the lock body is limited by engagement of the shoulder with the bottom of the annular flange.