¼” NPT to Second Stage Fitting This adapter has ¼” npt male on the one side and a second stage fitting on the other. The second stage end is the same as your scuba regulator second stage (unless you have a Poseidon Regulator). With this adapter you can take your scuba regulator hose and make it ¼ npt. This allows you to use standard scuba hoses for specialty applications such as rebreathers, wet subs or my favorite tinkering!!!