The BA13 is color coded orange to identify it as aNissan brake adatper.  The “probe” style design attaches to the brake fluid reservoir in place of the reservoir cap.  The serrated black nut is rotated to expand the probe o-ring inside the reservoir neck creating a pressure tight seal.  Adapter Part for Brake Service Tool (BST32 and BST64). Other brake service machines using the “Tru-Flate” style connector This is sold as a single adapter.

Adapter Chart