Glad Jerry pointed this out - may help preserve a few more old cranksets... for me, of course.
~ There was another clever part on these tools, although really not seen in this photo. The back/closed side of the socket had two rectangular prongs. These were sized and spaced perfectly to fit into the slotted alloy crankarm dustcovers, so they could be removed or replaced without damaging them. - The alloy on those caps was soft enough that enough fidgeting with large screwdrivers or other handy but improper "tools" would eventually gouge them out very badly. Perhaps why the dustcovers are now so scarce, although 49D cranks are plentiful.
Bob Hanson, Albuquerque, New Mexico, USA