A flour dredger looks like a large salt shaker, but it is designed for sprinkling flour. The holes in it on the top are wider than they would be for a salt shaker.
They consist of a base in which you store the flour, and a top that you screw on. The top has the holes in it. Some have a handle on the side, some don’t. Most are made out of aluminum.
You can also use a flour dredger to sprinkle cocoa powder, icing sugar, dried herbs, etc.
Some fish and chip shops use these for sprinkling salt over large batches of chips.
To use, you turn it upside down, and shake gently, moving as appropriate to distribute the flour evenly over the food surfaces that you want to sprinkle.
After use, you store it away, and refill with flour as needed from time to time.
Flour sifter, sieve, or your hands.
Flour dredgers have been made at least since the late 1800s.