Go to a hardware store and get the size bit you need that is made for metal. Most cast iron isn't really hard unless it is white cast iron. If the hole is over 3/16, pre-drill it with a small bit first. It might be a good idea to use some cutting oil to.
For more info, see the section on calcium absorption. High calcium foods include dark leafy greens, cheese, low-fat milk and yogurt, bok choy, fortified tofu, okra, broccoli, green beans, almonds, and fish canned with their bones. The daily value (DV) for calcium is 1000mg.
Calcium carbonate, nature's most concentrated source of calcium, delivers 500 mg of elemental calcium in each VIACTIVâ¢ Calcium Soft Chew. The calcium in VIACTIVâ¢ has been clinically demonstrated to be absorbed as well as the calcium from low-fat (1%) milk.