NASA astronaut Mark Vande Hei and Japan's Norishige Kanai ventured out Friday to complete the job that began last October.
The 58-foot robot arm had both of its aging mechanical hands replaced on previous spacewalks.
Friday's work involves bringing one of those old hands inside so it can be returned to Earth for a tuneup, and moving the other gripper to a long-term storage location outside.
This last spacewalk in the series should have been completed by now, but was postponed because of complications with the robotic hand that was installed last month.
Further delays were caused by this week's late arrival of a Russian supply ship.