What you call salt boxes, we in Zild have usually called salt cellars.
We have salt cellars, too, Max ... I have glass ones and fancy gold ceramic and even a pair in silver ones for the table on special occasions.
Salt cellars also come in pairs that are sometimes made as miniatures of other things -- people sometimes have collections of them -- Considered "collectables" there is everything imaginable from Mickey and Minnie Mouse and other cartoon characters to pairs of Moose to Hansel and Grettel,to bull and cows, to cars, to lobsters and I even saw a pair of frogs once! None more than about four or five inches tall.
The salt holder in these types of salt cellars has larger holes than the pepper shakers, or sometimes there are just more holes in the salt cellars than in the pepper. Makes for a surprise, sometimes, for the uninitiated!
