What does D rung ladder mean?

What does D rung ladder mean?

Ladder rungs are either flat, round or “D” shaped. Stepladders use 3″ or greater channels for flat steps. “D” rungs are preferred for step/extension and straight ladders. Their flat top surface is more comfortable to stand on. Rungs must be capable of carrying an 800-LB. Mar 28, 2018

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