Stem or stroke work equally well for the 7, while bowl would be appropriate for the 6:
http://www.infor.uva.es/~descuder/docencia/IG/letterform_anatomy.pdf

Thanks but then what would I call the horizontal part of the ‘7’? Or the vertical link in the ‘5’? And how would I begin to talk about the various parts of the figure ‘8’ it’s not really something they cover in any article on type anatomy…

And for the ‘6’ how would you contrast that with the part that descends to form the upper left side of the glyph

Right or Left, Across or Down, Top or Bottom, Diagonal or ?!

the loop loop or eye, the line line, leg or arm @ the curve horn or tail?!

I'd call the horizontal part of the 7 the arm, the "vertical link" in the 5 the stem, and the sections of the 8 the upper and lower bowls (they both enclose a counter).

As for the 6, the part that isn't the bowl would be called the stroke.

Kelvin, I’ve never come across the information you seek.
Therefore (somewhat vainly) I assume it does not yet exist—terra incognita waiting to be named.
Why don’t you make a diagram with call-outs, as per Aziz’ example, of what you think would be appropriate?

hmm. I’m not a fan of extending the term ‘stem’ to anything vaguely vertical, as I think it should be reserved for vertical, stressed strokes. A few terms already exist—I know the horizontal part of the ‘5’ is called the flag, but as far as I know nobody has ever named the other numerals’ parts. Here’s what I came up with?