for example in a date do i use emdash or endash ” 17-05-09”

In this case I would use neither, instead use a regular dash, or if you can, a figure dash.

also for example on a poster say an expo runs from 17 “until” 20 march 2009 (meaning that actualy the expo ends on 19 march. do you use en or emdash between “17 and 20”)

Here you would use an en dash. En dashes are used anytime you have something in a range (times, dates, etc.).

As far as em dashes go, you use them mostly in body text when interrupting a train of thought.

Patrick

'Trick, that's exactly how I use en dashes: from-to, but not within a phone number, ISBN/EAN, zip code, or date. I also use it in the sense of "contrary to": "the blood–brain barrier", "human–robot interaction" (as opposed to a 'human-robot').

Am I right in remembering English style train of thought is interrupted by space-en dash-space, while Americans interrupt using the em dash solus (w/o spaces)?

>Am I right in remembering English style train of thought is interrupted by space-en dash-space

We use emdashes here but I think we put thin spaces in if the emdash doesn't have generous sidebearings.

Ah -- 'here' being the UK, I see in your profile. (Well, unless you moved :-))

Just for posterity's sake: Spanish is space-en dash, interruption, en dash-space. Anyone know more?

hey thnx for replying....mmmm afraid its getting a little confusing :D

Just to get this straight:
-
hyphen

–
en-dash

—
em-dash

An exception to what I mentioned about spacing from the Penguin Guide to Punctuation:

...in the rare case in which a sentence is broken off abruptly without being completed, a single dash is also used:

 General Sedgwick's last words to his worried staff were
  'Don't worry boys; they couldn't hit an elephant from this dist—'.

Note that, in this case, the dash is written solid next to the unfinished piece-of-a-word which precedes it.

Am I right in remembering English style train of thought is interrupted by space-en dash-space, while Americans interrupt using the em dash solus (w/o spaces)?

That is certainly what I do in documents – described in Bringhurst as ‘a phrase marker’ in a sentence with normal word spaces. I have seldom used an em dash except when I found the en dash too narrow.

However, to indicate 17–20 March (meaning something runs from 17th until 20th March inclusive) I use an en with no spaces. For a date as numerals I would use 17/05/09 although that might change if using non-aligning numerals as here.

Bringhurst also mentions the three-to-em dash (which I have never used), he also gives a pithy criticism of the em dash as belonging in “the padded and corseted aesthetic of Victorian typography”.

Tim

When typsetting a book, or a text in a paragraph document, I prefer en dashes, in dialogues or in the middle of a sentence. Like this:

The same text with em dahses looks weird. The em dashes are too wide (it also depends on the the typeface you're using), and deleting the blank spaces doesn't help:

In names and numerals/dates, I prefer using the hyphen, without blank spaces, instead of en dash; for the same reason: en dash in this case looks too wide: