Special Valve Connectors
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 1998 Pontiac Trans Sport, 1998 Oldsmobile Silhouette, 1998 Oldsmobile Bravada, 1998 GMC Yukon, and 1998 GMC Suburban. However, it is still accessible from the selected car via links, so may be relevant.
On some General Motors models, thread size on high-side service valve (3/8" - 24 threads) is different from thread size on low-side service valve (7/16" - 20 threads). Special adapters are required to make this connection. See Fig 1. These adapters are available in 45-degree and 90-degree angles in addition to straight-fixed and flexible adapters.