In my experience, the larger the box, the faster that Registered Mail will travel, apparently because post offices hate having space hogs in their safes, locked cages, locked offices, locked vehicles, and the other small, secure spaces wherein Registered Mail is stored.
The 12 X 12 X 12 box is the largest that you can go without paying gigantic surcharges for longer distances (any dimension over 12 inches causes postage to skyrocket). They are definitely worth the mere $2 or so.
Comments
Thanks for being helpful.
Steve