Inside Diameter (ID) 1 : The internal diameter of a tube, conductor, or coupling, as distinguished from its OD (Outside Diameter). Fire hose sizes are classified by a nominal internal diameter
National Wildfire Coordinating Group (NWCG), Glossary of Wildland Fire Terminology, NWCG Program Management Unit, National Interagency Fire Center, Boise, ID, USA 2014. http://www.nwcg.gov/pms/pubs/glossary/pms205.pdf, (For Fr - Amer) {45}