Liftmaster 8500 part?

Hello, new to the forum, my son was screwing around with my garage door when I was at work, and of course broke the opener.  I took it off and imediatly saw that there was a broken part.  It is a white sleeve that sits in front of the wicker spring, and seems to operate like a clutch on the clamp bar with the sprocket.  Does anyone know what this is called, I cannot find it anywhere on the website or even online.  It seems to be the only part not labeled on the parts diagram.  Any help would be much appreciated!  I colored the part green (Kinda). LOL the image is linked below.

Thanks,
Joe

https://www.dropbox.com/s/a6kbvmawulv5nke/Screen%20Shot%202019-01-04%20at%2012.00.44%20AM.png?dl=0