The fitting shown has a push on tube connector and the other end of the fitting is national pipe thread(npt). If you want to use ss hard line then use something like Swagelok compression fittings that have the correct ss tube size and npt. You do have to use a flexible tube or hose whereever there is connection that is subject to movement from a stationary point. (ie. engine mounted compresser to the frame or body).
http://www.swagelok.com/product.asp?...NGS&GroupDesc=