I need the name of this ring for my Tamron 17-50 2.8 lens

So guys,
my lens is Tamron 17-50 F2.8 for Canon.
(I did not find any suitable place to post, so if any moderator can please move this thread to appropriate section please)

My lens had some spots in front element. I was watching a video on youtube on how to remove the front element and clean it. It looked easy. but i when opening that front ring, i broke it.
Please have a look at this picture, and tellme what does it call?

I have searched all over the internet for this but couldn't find any help.

If anyone of you please share a link where i can find one on Ebay or Aliexpress. that would be great.
Thanks
Cheers

I may not be of any help, but I've always called it the front element retaining ring. There's even a special tool to remove it safely. As for replacing it, I would contact Tamron and see what they have to offer.

Sorry I can't be of more help.

It used to be that you could call Tamron at 631-858-8400, select option 3 for parts and then leave lens model and fax number and you would get a parts list by fax. I know the phone number is still good, so start there and work your way to "parts".