In the 90's some regulator manufacturers (notably Apeks, Aqualung, and Mares) started offering some versions of their first stages with an oversized 1/2" low-pressure port. The oversized port has an optimized gas flow path and should be used to supply the primary second stage. (Mares calls it a DFC port.) While the oversized and optimized port does slightly improve machine test results in simulations, most divers found it does nothing significant for actual in-water breathing performance and also inconveniently requires a non-standard regulator hose.

Today, most manufacturers have deprecated their oversized port on first stages for the recreational market, although it continues to be available on versions for the military market. If you are seeking a 1/2" regulator hose, instead your best strategy might be to just plug the oversized port and use one of the other standard size low-pressure ports. If you insist on a regulator hose with a native 1/2"-20 UNF fitting, then take a look at these non-standard regulator hoses.