These are particularly good Japanese-made kenzans (also called frogs or spiked flower holders).
Each one has brass needles molded into a weighted alloy base. All parts are non-corroding. The needles are straight and accurately positioned, unlike many cheaper styles.
The kenzans are particularly suited to ikebana, a Japanese style of flower arranging that emphasizes symmetry and simplicity; however, they can be used for almost any style of floral arrangements.
To use, cut stems on the diagonal and insert directly into the needles. Very thin stems can be supported with additional short pieces of the same material.
Sizes are approximate. A little kenzan goes a long way.