Final answer:
Lubricant for a ball-bearing joint is not a direct material because it is used to maintain machinery rather than being part of the actual product, whereas the plastic for a PC case and steel for tires are direct materials.
Step-by-step explanation:
The question pertains to identifying which item from the given list does not qualify as a direct material for a product. In cost accounting, direct materials are those that can be directly traced to in the production of a specific product. As per the provided options:
- Lubricant for a ball-bearing joint for a large crane would be considered an indirect material because lubricants are generally used for maintaining machinery rather than being incorporated into the product.
- Plastic used in the covered case for a home PC is a direct material as it becomes a part of the final product.
- Steel used in the manufacturing of steel-radial tires is also a direct material because it is a primary component of the product.
Thus, the lubricant for a ball-bearing joint is the correct answer as it is not a direct material but rather a supply used in the production process.