Drag link socket. The way the drag link is assembled, it has to be taken apart to be removed from the steering and pitman arms. There's a plug in the end of the housing, should have a cotter pin securing it in position, that has to be removed. It has a slot in like a larger screw. The special socket is designed to allow not only for removal, but also proper installation and preload adjustment.
Figure 43, which is of the tie rod, shows how the drag link ends come apart. They are virtually identical in construction.
