Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3559874.

6/27/2019 - I made the clip very slightly thicker. I think it is an improvement.

The locking collar on the top of the hot end keeps the PTFE tube from slipping out. The lock is only effective when it is lifted away from the hot end. When down the tube is unlocked. The frequent ejection and retraction of the filament during printing can cause the PTFE tube to come loose if it is not locked in position.

To keep the lock working a small clip is placed between the hot end and the locking collar.

The small and easily printed part can save trouble in the future. You can buy them from Bondtech or just print your own using PET.