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.
Other foods that are high in calcium include: 1  Spinach. 2  Kale. 3  Okra. Collards. 4  Soybeans. White beans.  Some fish, like sardines, salmon, perch, and rainbow 1  trout. Foods that are calcium-fortified, such as some orange juice, oatmeal, and breakfast  cereal.
Milk, yogurt, and cheese are the main food sources of calcium for the majority of people. Milk also has added vitamin D, which is important for helping your body better absorb calcium. Calcium can also be found in leafy, green vegetables. Kale, broccoli, and Chinese cabbage are good vegetable sources of calcium.