Double ferrule tube fittings are the most common style of instrumentation fittings, and they can also be purchased in brass materials.
Brennan Industries, N2650-04-04-04-04-SS
Brennan Industries - PARTcommunity 2D/3D Models
Double-Ferrule Tube Brass - Brennan Industries - Download 3D CAD
5405 Tube Fittings and Adapters by Brennan Industries
Brennan Industries NS2403-04-04-B Brass Straight Single-Ferrule
Brennan Industries N2503-08-08-B Brass 45 Degree Elbow Double
Straight Brass Fittings PL-MIFS Straight
Brennan Industries Instrumentation Double Ferrule Tube
4604-O Tube Fittings and Adapters by Brennan Industries
Brennan Industries N2705-LN-08-06-B Brass Straight Double-Ferrule