What is the required average inside diameter for a 4" mold used in standard proctor tests?

For a 4-inch mold used in standard Proctor tests, the required average inside diameter is specified to be 4 inches with a tolerance of ±0.016 inches. This precision is necessary to ensure that the mold consistently meets the standards set for compacting soils in a controlled manner. The Proctor test is sensitive to the mold size because even slight variations can affect the compaction density and, consequently, the results of the test. Maintaining the specified diameter within the defined tolerance allows for uniform compaction efforts across multiple tests and ensures that the laboratory results are reliable and reproducible.

The other options present diameters that deviate significantly from the required 4 inches, either being smaller or larger than what is acceptable for the Proctor test, which would not yield valid results per the test specifications. Thus, the tolerance range is crucial for the accuracy and effectiveness of soil compaction assessment.