Selecting the right coupling depends primarily on the regional standard used by the local fire department. Common types include Storz (Germany/Europe), NH/NST (USA), British Instantaneous (BS336), and Machino (Japan). You must verify the nominal diameter (DN) and pressure rating (typically PN16 or PN25) to ensure compatibility with existing hoses and hydrants. For industrial use, forged aluminum is preferred for its strength-to-weight ratio, while brass or bronze is essential for marine environments to prevent saltwater corrosion.