50 CFR § 665.265 - Size restrictions.
The height of a live coral specimen shall be determined by a straight line measurement taken from its base to its most distal extremity. The stem diameter of a living coral specimen shall be determined by measuring the greatest diameter of the stem at a point no less than 1 inch (2.54 cm) from the top surface of the living holdfast.
(a) Live Hemicorallium laauense, Pleurocorallium secundum, or Corallium sp. harvested from any precious coral permit area must have attained a minimum height of 10 inches (25.4 cm).
(b) Live black coral harvested from any precious coral permit area must have attained either a minimum stem diameter of 1 inch (2.54 cm), or a minimum height of 48 inches (122 cm).