Sometimes the diameter is dictated by the couplings as they will only come with a set size tail. Eg. The biggest tail on a Nakajima 50A will be 52mm (2”) therefore 2” hose will be needed to use this coupling.
A common problem is that people measure the hose flat and think this is the diameter, but is not the case. Click on the PDF datasheet below to work out the size.
Hose diameter conversion datasheet
The couplings are available in both light alloy or Gunmetal/Brass however most marine customers will want the Gunmetal/Brass couplings as this is more suited to the salt water and harsh environment were as Light Alloy will corrode in time.
Couplings are generally wired on to the hose as per the BS 6391:2009 Standard. This states that 2.5” Instantaneous Couplings to BS 336 are tied in by binding (’bound in’) with galvanized mild steel wire of a diameter 1.6mm and applied over a hose guard of synthetic fibre. However this only applies to BS 336 Couplings (2.5” Inst) but is still good practise to wire the coupling on. Other couplings such as Storz and other European fittings are commonly wired on without guards. Also multi serrated type couplings must be secured by 20 continuous turns of wire and ribbed type couplings by at least eight continuous turns on both sides of the rib.
There are other ways of fitting the couplings to the hose for example using clips etc, however we would always recommend that couplings are fitted using wire.
International hose couplings datasheet