The three most common types of relating devices are relating cables, _______ and _______.

The three most common types of relating devices used in hoistway maintenance are relating cables, mechanical lever linkage, and chain and sprocket systems. Relating cables are essential for the effective operation of elevators and similar machinery as they help transmit force and maintain alignment.

Mechanical lever linkages provide a means of transferring motion from one point to another within a system, often allowing for changes in the direction of force. This mechanism is crucial for precise movements and operations in elevators, where it aids in the control of various components, such as doors and car movements.

Chain and sprocket systems are widely used for their reliability and efficiency in power transmission. In hoistway applications, they allow for the movement of heavy loads over distances with less wear compared to other types of systems. Each of these devices plays a significant role in the smooth functioning of hoisting equipment, ensuring safety and operational efficiency.

The other options include devices that may not be directly involved in the relationship or motion transfer needed in hoistway systems or are not as commonly recognized as the primary relating devices in this context. Thus, understanding the role of mechanical lever linkages and chain and sprocket systems alongside relating cables highlights why this combination is commonly referred to in the field.