Bohrung - Kunststoffverteilern mit einer Bohrung
a port is pretty logical in this description

3-6 A minimum 12-inch-long (305 mm) by 0.060 inch-thick (1.52 mm) steel scleev shall be centered in each duct opening.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

k) A duct opening may not be located where the natural flow of air is unduly obstructed, adjacent to possible sources of vapor ignition, or where exhaust air may be taken into a supply duct.
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c) The total inlet area and the total outlet area of each ventilation duct may not be less than one square inch for each foot of beam of the vessel.
https://books.google.de/books?id=Krc8AAAAIAAJ&pg=PA272&lpg=P...

10 inch Round Diffuser Air Vent Ventilation Duct Opening HVAC Register Grille

The H800-06 is a 6 in. round air diffuser. This step down ringed diffuser is used to cover duct openings. Our product is constructed to ensure maximum airflow and compliment your home decor.
https://www.ebay.com/itm/10-inch-Round-Diffuser-Air-Vent-Ven...

Note: Each air duct opening shall have a free area of not less than 1 square inch per 2,000 Btu/h of the total input rating of all equipment in the enclosure.
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

Need New Registers?
Accord ABFRBR410 Floor Register with Louvered Design, 4-Inch x 10-Inch(Duct Opening Measurements),
https://dengarden.com/home-improvement/how-to-clean-ventilat...
(Note: Not all ducts are round, but rectangular as well)

Duct systems should be designed to have air flow through the ducts with as little friction or resistance as possible. The amount of air that flows through a duct depends on the cross section area (duct opening area) of the duct and the air speed.
http://www.ccohs.ca/oshanswers/prevention/ventilation/ducts....

Just an alternative suggestion....
Bore: the hollow part inside a gun barrel or other tube.