Which of the following is a type of joint for steel piping?

A restrained joint is specifically designed to hold pipes together in such a way that they can resist movement caused by internal pressure, ground movement, or other forces. In steel piping systems, these joints are crucial for maintaining system integrity, especially in environments where there may be substantial shifting or forces applied to the pipes.

These joints might incorporate various mechanisms, such as bolts or other locking devices, to secure the joint between sections of piping, preventing them from separating under stress. This is particularly important in water distribution systems where pipe failure can lead to significant service interruptions or water loss.

In contrast, the other options do not refer to common types of joints specifically utilized in steel piping applications. For example, a flexible ball joint is not typical for steel piping due to its rigidity requirements, while rubber gasket joints are generally associated with other materials and not designed to accommodate high pressures. A galvanized steel ring can be a component of some joints or fittings, but it is not classified as a joint type itself. Thus, the restrained joint is the most accurate answer regarding its role and functionality in steel piping systems.