I started with a 30" long, 1" x 4 3/4" scrap of reclaimed wood, and five zinc pails. I put the far right and far left nails in the middle of the board about 3" in from the ends, then about 6" apart on the the other three. Or at 9", 15", 21" and 27".
I used nails about 2 1/2" long. You can see they stick above the board a bit.
I also put a little thicker nail through the center bottom of each pail for drainage and to anchor them onto the board.
The nails keep the pails from moving around on the board. Since the hole in the pail is larger than the nails in the board, there will be room for drainage. The pails are loose enough to fall off if tipped over. Otherwise they will stay put, and will not be moved by wind or if the potting sink is bumped.
Next I filled the little pails with potting soil and sempervivum (hen and chicks). The board covers the faucet holes in my potting sink perfectly.
Now the hen and chicks need a little warmth and sunshine to grow.