In the term (D/d ratio) the d is an abbreviation for:

The term (D/d ratio) is commonly used in rigging and other engineering fields to refer to the relationship between the overall diameter of a load (D) and the diameter of the ropes or lines being used (d). In this context, the letter 'd' specifically stands for diameter. Understanding this ratio is crucial as it helps in determining factors such as the effective strength of the rigging system and the optimal configuration to ensure stability and safety during lifting operations.

When considering this ratio, knowing that 'd' represents diameter allows riggers to assess whether the chosen lines or cables are appropriate for the particular load diameter they are working with, ensuring that the rigging setup adheres to safety standards and operational performance requirements.