My port side engine has a loose alternator belt, and the alternator is
at the outer limit of its adjustment. I took a look at the belt today
hoping to find some markings on it regarding size, type, etc. No
luck. Short of removing the belt and taking it to a parts dealer, is
there any other way of sizing this thing? Who makes the best belts in
terms of durability? Are there different grades, and if so, how are
they specified?

Thanks in advance.