I slice this thing from the other direction: Numbers whose names consist of a single word should be spelled out IF:
You may note that I discern here between digital numbers (counts) and analog numbers (measurements). How many fingers do you have? That's digital. The number is probably between one and twelve; most of us have ten. How much do you weigh? I'm about 14 stone, or 196 pounds. How much does my hat weigh? About 6 ounces. Modern newspaper style would have it as six ounces, and while that's not exactly wrong, it's not exactly right either. If it turned out to be 6.1 oz. you would have to change the style to make the adjustment, which is a clue that the wrong style was used.
Since the terms 'digital' and 'analog' are bandied about so much nowadays, I think it's high time we understood a little better what they mean.
I have a "frammis", a "widget", and a "frob", none of which are lustrous.
I have a "frammis," a "widget" and a "frob," none of which are lustrous.
Can you honestly tell me that the second line reads better?
The second line also has another traditional aberration, that of leaving off the comma from the penultimate item in a list when followed by 'and'. OK, here's the deal: a clue to where commas go is to consider them "timing marks" -- and when you think about them that way you can write and parse things like "I have a tennis racket, a bat and ball, a pair of snowshoes, and a pogo stick.". Read it out loud and note that there are little micro-pauses at the commas.
Note also the double periods in the example above. This is totally nonstandard, I know. I am not advocating this style, as it looks too much like a booboo, even to me. But it works; there is no doubt that the quoted sentence ends, and the enclosing sentence ends there too. It's something to think about. Punctuation is not an exact science; it's an evolving art.
See also "Punctuation Liberation Front" on this same website.