FPV antennas are commonly mounted on 3, 4 or 5 mm coaxial wires. It is often necessary to bend the coaxial wire 90 degrees to match the application. Some coaxial cables stay bent, but most are extremely reluctant and will slowly return to a 45 degrees angle, no matter what you do.
This design is a very simple solution to the problem. Print the bend that matches the thickness of your coaxial wire, insert the wire and then clamp it down using two small zip ties. Problem solved.