Hola Tom,

I’d recommend that download a good on-line dictionary like WordReference. They even have an app, and it is free.

Un llave de paso [ball valve]; 

Roscar is the verb to thread [cut a thread onto] a piece of metal  i.e to make a screw for example; a thread [noun] is rosca. I imagine it would be rosca interior, y rosca exterior.  I don’t know if the “feminine / masculine” adjectives apply in technical language in the way that they do in English to describe the nature of connectors and joints and the like. Hope that helps. John