Brass Push>Connect Metric Tube Fitting, 6.00 mm Tube OD To 1/8-28 Male Universal BSPP/BSPT, Straight

Compressed air is actually one of the main uses for this fitting. It's built for pneumatic instrumentation lines, along with lubricant and cooling lines. The brass and nickel-plated construction holds up well in those environments, and the Buna-N o-ring seal keeps things tight. Pressure rating tops out at 250 psi depending on tube size, so it covers most standard compressed air setups without any trouble.

Tool-free is the whole idea on this one. It is a push-connect style fitting, so you make the connection by pushing the 6.00 mm tube into the fitting, and the Buna-N O-ring handles the seal. It is also made to be reusable, so you can disconnect and reconnect without needing extra tools.