Good point/question.
I think the alphabetic terminology can be applied well enough
to the numerals. The conventional unconventional :-) "stroke"
contrast might indeed warrant some specialization though.

hhp

Right.

Therefore, the two kinds of four are open and closed counter.

The horizontal stroke at the baseline of sans serif “one”s is a crossbar, not a serif.

**

However, there are no established terms to distinguish between oldstyle “one”s that have majuscule “I” configuration, and those which have minuscule “l” construction.

There is also no term for the quite odd variant of oldstyle “zero” that is light in weight, circular and without contrast.

And again, the variants of “three” — with the top half composed of either one curved or two straight strokes — have no special names.

There is also no term for the quite odd variant of oldstyle “zero” that is light in weight, circular and without contrast.

I'd call that a monoline zero.

> The horizontal stroke at the baseline of
> sans serif “one”s is a crossbar, not a serif.

It's interesting however to consider the contrast with serif fonts.
Is my impression correct that virtually all serif fonts make it look
like serifs and not a bar?

For the three: the flat-top style could be called the Ezh
or Dram form. http://en.wikipedia.org/wiki/Ezh_%28letter%29
BTW, there's also a very rare form of three where the
top is flat but it's joined to the bottom with a curve.

hhp

In fact, there is jargon for the flat-topped form of three; it is a "banker's three", which I believe means that it was the preferred form in handwritten accountancy to distinguish it from a sloppy two. That said, "pointy three" and "rounded three" serve me fine and laymen understand them.

I accept that the serif-analogues on "I" and "1" in sans faces are "bars", but not necessarily "crossbars". "J" can be capped with such a bar, and there are forms of "J" that also have an actual crossbar, in the middle. I've seen "barred I" before. If they need a specific name of their own, and I think they do, "endbars" could work.

The (usually) sloped thing on the top of a "1", be it a serif or not, may be sensibly called a "beak" and so any form that has it would be "beaked".

I've heard the top of a 1 and 5 called a 'flag'.

And I've heard the banker's three originally prevented it being converted into an eight when written on a cheque.

Does anyone have terms for a 2 that does the Helvetica thing of changing direction on the spine rather than coming straight to an acute angle at the bottom?

The “Cobra move” or the “Swan neck”? ;-)

The subject line refers to 'Arabic characters'. Is this intended to mean so-called Arabic numerals -- which the Arabs call Indian numerals -- or to Arabic letters also?

I kinda recall seeing the flat-top three and the barred seven called French three/seven. Also, I think that the old-style numeral 1, when it looks like a squashed I, is said to be 'roofed'. But, I could easily be wrong on both counts.

Nicely clarified, Kevin.