I have part of an old Hardinge milling attachment probably for a Cataract that I dug out of a box of my grandfathers shop stuff. The base is very similar to the one shown on the Lathe UK site with a few tiny differences: milling attachment
Aside from the dial shape and the obvious fact that an attachment is missing from the front, the center stud is much shorter and bigger around than is required to hold the gear reduction milling attachment shown in the link above. The shape of the stud and the small hole above the center of the stud lead me to believe that this unit may have held something different than the gear unit shown. I can see the small hole acting as a stop to set an attachment at the zero position. As other manufacturers had made milling attachments that were simple vice jaws, did Hardinge ever have one in their catalog? I find it strange that they wouldn't but aside from the Lathe UK site I can't find any information.