The cross-section dimension refers to the smallest cross-sectional measurement of the log or timber at any point along its length. Logs measuring 15 cm or more at their smallest cross-section fall into the larger-size subheadings, while those measuring under 15 cm at any point fall into the smaller-size subheadings. Consistent measurement methodology is important for accurate classification.

Treated wood in the rough (440311 for coniferous, 440312 for nonconiferous) has been impregnated with paint, stain, creosote, or other preservatives. Untreated logs — even if bark has been removed or the wood roughly squared — fall under the species-specific subheadings. The presence of a preservative treatment is the key distinguishing factor.