In what scenario is clearance fit always applicable?

• A. When there is a binding between two parts
• B. When there is no motion allowed between mating parts
• C. When there is a clearance between the axle and the opening
• D. When parts are permanently assembled

Answer: (C)

Clearance fit is a type of fit that ensures a space between two mating parts, which allows for relative motion or the ease of assembly. This scenario is specifically applicable when an axle fits into an opening with sufficient space around it, enabling it to rotate freely without any interference. The purpose of clearance fit is to prevent binding and allow for adjustments, expansions, or thermal movements.

In the context of the other options, binding between two parts suggests an interference fit, which does not allow any clearance and would not be applicable for a clearance fit scenario. When no motion is allowed between mating parts, a different type of fit such as a press fit might be required, which again does not pertain to clearance fit. Finally, permanent assembly of parts leans more toward solid, interference fits rather than the space and movement facilitated by clearance fits. Therefore, the scenario where there is a clearance specifically aligns with the definition and purpose of clearance fit.