These are world's best teflon UX4 sockets and we've tried all kinds over the years. These have a spring retainer on the OUTSIDE of the pin gripper so never come loose with repeated insertions. These are CNC'd from one solid block of teflon and give the best damping against chassis born vibration and resonance. Pins grippers are silver plated and grip with much more force than standard UX4 sockets.