This is totally not related to what I have posted in the past, however I could not find this information in my Internet searching so I decided to post this for anyone else who may need it.
Here is the inside of the "KONG® On The Go Reflective Palm Retractable Dog Leash" and some key components.
3. Remove the cover to expose the insides. Be careful not to drop the spring or ball.
4. The spring sits in a 'seat' on the track of the thumb button.
5. The ball sits on top of the spring and is responsible for 'locking' the thumb button into place against the leash reel.
6. The thumb button sits in its track.
The reason I posted this is because my daughter walked my dog and somehow the leash came apart. I took it apart and put it back together and the thumb button would not lock into place. I took it apart again and determined something was missing. Something needed to sit on/with the spring and engage the thumb button when it slides. I tried a few things I had lying around and it did not work.
I later asked my daughter about it and she said "Oh yeah! There was some piece that I put in your office." And it was the ball that sits on the spring. Problem solved.