Brass Push>Connect Metric Tube Fitting, 8.00 mm Tube OD Union

The collet ring is what does the work. When you push the tube in, the collet grabs and locks it in place under pressure. To get it back out, you just squeeze that collet ring with two fingers and pull the tube free. No wrenches, no thread tape, nothing extra. It holds up to 250 psi and can handle vacuum down to 29.5 inches of mercury, so it's not just a light-duty convenience fitting.

For joining two cut ends of 8.00 mm metric tubing in a straight run, this Push>Connect union is the right style. You push each tube end into the fitting to connect, and it uses an internal O-ring seal.