Cast iron piping was traditionally made with one "spigot" end (plain, which was cut to length as needed) and one "socket" or "hub" end (cup-shaped). The larger-diameter hub was also called a "bell" because of its shape.
In use, the spigot of one segment was placed into the socket of the preceding one, and a ring of oakum was forced down into the joint with a caulking iron. Then the remainder of the space in the hub was filled up. Ideally, this would be done by pouring molten lead, allowing it to set, and hammering it tightly with a caulking tool. If this was not possible due to position or some other constraint, the joint could be filled with lead wool or rope, which was forcibly compacted one layer at a time.
This labor-intensive technique was durable if appropriately done but required time, skill, and patience for each joint to be made up. Quicker and lower-cost methods, such as rubber sleeve joints, have replaced mainly leaded hub connections of cast-iron piping in most new installations, but the older technology may still be used for some repairs. In addition, some conservative plumbing codes still require leaded hub joints for final connections where the sewer main leaves a building.