2002 Astro R-134 HP quick disconnect port

I went to check my A/C pressures with the new A/C gauges I just bought and I can't get the quick disconnect fitting to latch onto the Asto High Pressure (HP) quick disconnect port. It fits on the port, but won't latch. The gauge quick disconnect fits and latches properly to my Grand Marquis and my Galant, but not the ASTRO. I can attach to the Astro LP port fine. Did GM make specially designed fittings on their HP ports, or is there probably a design defect?

The company that makes the gauge kit sent me a replacement - it snapped on perfectly. The old gauge fitting was apparantly slightly defective.