What does a clearance fit ensure when assembling parts?

A clearance fit is a type of fit that specifically ensures there is always some space between the assembled parts. This design allows for the parts to move freely in relation to one another, which is crucial in applications where parts may require relative motion without binding or interference.

Clearance fits are typically used in situations where ease of assembly and disassembly is important, such as in rotating shafts or sliding mechanisms. The intentional space can also help account for factors like thermal expansion or manufacturing tolerances, which could otherwise impede proper functioning if the parts were too tightly fit.

In contrast, the other choices imply qualities that are not characteristic of a clearance fit. For instance, a fit that ensures parts are tightly together would fall under the category of interference fit, which is designed for parts that need to stay securely together without play. Permanent bonding suggests a more rigid connection than a clearance fit allows, while a fit that mandates a single orientation is more characteristic of localization fits that are deliberately designed with specific alignment features. Therefore, the essence of a clearance fit is its guarantee of a gap between parts, making option B the correct explanation.