What is the term used to describe a material that prevents the penetration of fluids in mechanical applications?

The term used to describe a material that prevents the penetration of fluids in mechanical applications is "sealant." Sealants are specifically designed to fill gaps and block the flow of liquids or gases, making them crucial in preventing leaks in various systems. They are especially important in applications involving plumbing, automotive, aerospace, and many other fields where fluid containment is vital for operational efficiency and safety.

In contrast, spacers are typically used to create distance between components, shims are thin pieces of material used to fill small gaps or provide support and leveling, and shackles are hardware devices used to connect two components, often in the context of lifting or securing loads. None of these options are intended or designed to prevent fluid penetration, which highlights the distinct role and function of sealants in mechanical applications.