I can't find your lamp in the catalogues, although it looks to have the same blank as No. 72 but a simpler cut pattern. Mine (shown below) is described as a No. 7 all glass 10" dressing table lamp (in a catalogue from September 1934). The dimensions for the No. 72 are not mentioned.
On mine, the hole is for an electric cable, as you can see. I would assume yours would be too, but 6" does sound very small. Are you certain that dimension is correct?
PS excuse the horrible pictures!-I opted for speed over beauty.