The generally accepted difference between the flight outer diameter and inner diameter of a hollow-stem auger is how many inches?

• A. 4-5 inches
• B. 1-2 inches
• C. 8-10 inches
• D. 0.5 inches

Answer: (A)

When you look at a hollow-stem auger, the inner diameter is the hollow bore inside the stem, while the outer diameter is the full width across the outside edge, including the flights wrapped around the stem. The gap between them represents the material thickness around the hollow core and the flight geometry. For common hollow-stem augers, that difference is typically about four to five inches. This reflects the combined wall thickness of the stem plus the depth the flights add to the outside diameter, giving you a practical sense of how large a borehole you’ll be creating and how much space the sample column and equipment will need.