6AN to Inverted Flare Fitting for Power Steering Line - Gear Box GM - Add 11/16-18 Inverted Flare for Return Side Only

These zinc-plated steel fittings will thread into the smaller pressure port on your GM steering gear box, and convert to a 6AN fitting size so you can make up a hose to your pump! 
Most OE steering gears have a 5/8-18 port for pressure, and a 11/16-18 for the return side. This is the case up through the late 1970's. Yours may be metric and use an O-ring inside to seal. The fittings you're looking at here, have an inverted flare seal. So you can visually see if your steering gear has a cone shaped bottom to confirm these will work. 
If the gearbox does not have an inverted flare, it is more than likely a later model (or aftermarket/Borgeson etc) box with a metric thread w/O ring bottom. These would require an M16 and M18 fitting also available from PTS.