The nipple is male threads (outside)while a coupler is female threads (inside). most online brew shop suppliers will carry them along with bargain fittings, weldless fittings, bobbym on here and many other places.
The piece in the pic with the teflon tape is a nipple.
............Alright Brain, you don't like me, and I don't like you. But lets just do this, and I can get back to killing you with beer......~Homer