Tensioners are mechanical devices used to maintain tension in a system, such as a belt or chain. They help ensure that these components operate smoothly and efficiently by preventing slack, which can lead to wear and tear or even failure. Tensioners are commonly found in automotive engines, where they keep the timing belt or serpentine belt tight. There are different types of tensioners, including automatic tensioners and manual tensioners. Automatic tensioners adjust themselves based on the system's needs, while manual tensioners require periodic adjustments by a technician. Proper functioning of tensioners is crucial for the longevity and performance of machinery and vehicles.