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I don’t know the name of the part. Is the metal bat, the one you have on left and one on right side of the speaker. And you clip the belt clip to it. After remove the cover I’ve find the screws witch screw the metal part but the metal bar get lost and I don’t know what is the name of it.

Thanks for respond. I’ve made the one missing myself and it’s not to bad compare to original one.

I would call it a strap latch or maybe a strap holding ring, strap ring, strap clip? Does that help?