This adapter would change a standard port to fit a low pressure hose that is a 1/2 male end. Older Apeks, Dacor and a few Mares hoses are like this. If you have upgraded your old first stage to a different version but you want to keep everything else from your reg set then this will solve that problem. Another option is if you want to go with a more economical hose that is on sale because it has a 1/2 fitting, this would make it work.
