Review on FJC 6015 R134A Refrigerant Adapter by Jon Lesperance

If you're looking to top up your car's AC and think an oil injector, manifold or vacuum pump "may" not work together, buy both a female and male counterpart as well. That "other people are buying this too" under whatever component you're looking at is probably filled with this and other fittings. They are inexpensive and fully correspond to the description.