Too right, don't just ask for one to suit your van/car etc, I've been stuck with a Fan belt that had been put back into the incorrect cardboard sleeve. Didn't know the length or belt# but the packet showed it was for the car I had at the time, ended up being too long. Have always kept an old one to take with me to the parts shop to check ever since.
Check it on the van before you leave, especially if you have replaced the original alternator as the pulley size may be different diameter, which will change the length required. Sometimes there is enough adjustment in the alternator support arm to compensate, sometimes there isn't
If you haven't change the fan belt for quite some time, but doesn't look too bad, put the new one on and carry the old one as the spare.
