Questions about Aquaracer automatic calibre 5

As Dave suggests its not the actual tightening down of the thread that provides the water resistance, its the multiple rubber seals themselves within the crown and stem, for that reason screwing it in doesn't require force or tightness.

Incidentally while its not recommended, and you should definitely screw down any crown that is capable of being screwed down, nearly all of them are still water resistant even when they are in the crown out position as the stem seal still keeps water out if its in good condition.

Oh and lastly, don't ever forget that your Aquaracer, like all water resistant watches is dependent entirely on those seals for water resistance. Whether its a $200 Seiko, a several thousand dollar Aquaracer Automatic, a Rolex Submariner, or a $26k Patek Philippe Nautilus, a set of tiny rubber seals is the critical factor and they need to be changed every 2-3 years and re-pressure tested to maintain water resistance.

Its the cheapest and most worthwhile thing you can ever do to a dive watch, and if you keep that up along with a reasonable service schedule your Aquaracer will be in fine condition decades and decades from now.