Clearance
Clearance is defined as the intentional difference in size between a hole and a shaft. It ensures that there is always a positive gap between the two mating parts, regardless of the tolerance range. In other words, the hole is always larger than the shaft, providing a clearance between them.

Interference
Interference, on the other hand, refers to a condition where the hole and the shaft have overlapping dimensions. It means that the hole is smaller than the shaft, resulting in interference or contact between the two parts. Interference fits are commonly used in applications where a tight and secure connection is required.

Transition
Transition fits, as the name suggests, are designed to provide a transition between clearance and interference fits. They are used when a slight amount of clearance is required under certain conditions and interference under other conditions. Transition fits allow for limited clearance in the tolerance range, but they do not always provide a positive clearance over the entire range.

Positive Clearance
A positive clearance is a condition where there is always a gap or space between the hole and the shaft, ensuring that they do not interfere or make contact with each other. This is particularly important in applications where relative motion or assembly/disassembly of parts is required. Positive clearance prevents binding, seizing, or damage to the mating surfaces.

Conclusion
Among the options provided, only clearance always provides a positive clearance between the hole and the shaft over the entire range of tolerances. It ensures that the hole is always larger than the shaft, providing a gap between the two mating parts. This allows for easy assembly and disassembly, smooth operation, and prevents any interference or contact between the parts. Transition and interference fits may have limited clearance or even interference in certain tolerance ranges, depending on the specific requirements of the application. Therefore, for a consistent positive clearance, clearance is the preferred choice.