What is a replaceable steel tube mounted in a case or housing called?

A replaceable steel tube mounted in a case or housing is known as a bushing. Bushings serve several important functions, such as providing a smooth surface for rotational or linear motion, reducing friction, and protecting the surrounding components from wear. They are commonly used in various applications, including machinery and automotive systems, where they facilitate movement and support mechanical structures.

In contrast, while a sleeve may sometimes be confused with a bushing, it typically refers to a covering that fits over another part but may not have the same function or replaceability as a bushing. A subframe usually denotes a secondary structure that supports the main framework, but it does not specifically refer to a tube or housing. Meanwhile, a socket is more often related to a component that connects to or houses electrical devices, rather than serving as a replaceable tube like a bushing does. Overall, the bushing's specific role as a replaceable component highlights its importance in numerous mechanical systems.