what piece of the hotend is this?

[lance-greene 7]

so i had to get a new hotend pack and heater element for my printer and in the bag was this little piece, i have the official assembly book and it doesnt show this piece

[IRobertI 516]

It is to prevent plastic from getting in between the nozzle and fan shroud:

http://support.3dverkstan.se/article/58-installing-the-ptfe-ring

[lance-greene 7]

wow the thing the ptfe ring solves is what happened to me