Tensioners are mechanical devices used to maintain tension in a system, such as a belt or chain. They ensure that the components remain tight and function properly, preventing slippage or wear. Tensioners are commonly found in automotive engines, where they help keep the timing belt or serpentine belt at the correct tension for optimal performance. There are different types of tensioners, including automatic tensioners and manual tensioners. Automatic tensioners adjust themselves based on the load and wear, while manual tensioners require periodic adjustments by the user. Proper tensioning is crucial for the longevity and efficiency of machinery and vehicles.