So if I said "hand me a couple of screws, would you?" - you'd give me exactly 2? If you know you want an exact number I would always use the exact number. I'd

So if I said "hand me a couple of screws, would you?" - you'd give me exactly 2? If you know you want an exact number I would always use the exact number. I'd never say "give me a dozen screws", I'd just say "give me 12 screws". Named quantities are almost always a range rather than a definitive number as far as I'm concerned.