These fittings are not quite as simple as it may seem. There are many different types of fitting profiles for compressed air.
Industrial Interchange ISO 6150 B (Blue)
ARO 210 (Yellow)
Japanese ISO 6150 C (Black)
European High Flow (Green)
All of these fittings are different and are not interchangeable. Since I was starting from scratch, I've chosen to adopt the European High Flow Standard. The reason for choosing this profile is the opening is the largest and has the least amount of parasitic loss.
What that all means is that if you begin to use the Euro High-Flow Prevost S1 Couplers the I'm offering, you'll also need to replace any existing plugs installed on your tools. These are inexpensive enough to easily do that.
Made of nitrided steel and are scratch- and corrosion-resistant
Comply with all the requirements of the prevailing standards, including the various applicable ISO standards.
NPT Thread type - they are not offered in stainless in NPT and would cost $20+ each if they did.
Both 1/4" and 3/8" male and female plugs fit the standard couplers I offer here in the store.