When selecting the appropriate shot blasting media, consider the following factors:

1. Material: The media's material should match the workpiece's material. For steel components, cast steel or stainless steel shots are commonly used; for softer metals like aluminum or magnesium, choose softer aluminum shots or plastic beads to avoid damaging the workpiece's surface.

2. Size: The size of the media particles affects the cleaning roughness and speed. Smaller shots can access smaller crevices and intricate details, providing a finer cleaning, while larger ones can more quickly remove thick layers of oxidation and rust.

3. Hardness: The media's hardness should be moderate, hard enough to effectively clean the surface without causing excessive wear. Hardness generally correlates with cleaning speed and media lifespan.

4. Shape: The shape of the media influences the cleaning performance. Round shots are typically more durable and distribute evenly, while cut shots or irregularly shaped media may provide better cutting action, suitable for removing stubborn contaminants.

5. Workpiece shape and requirements: Consider the workpiece's shape and cleaning requirements. For complex-shaped parts, specific shapes or sizes of media might be needed to achieve optimal cleaning results.

6. Economy: The cost and lifespan of the media are also factors to consider. More durable media may have a higher initial investment but can be more cost-effective in the long run.

In practical applications, it might be necessary to test different types of media to determine the most suitable one for a specific workpiece and application.