I loved the shower head until the washer or seal or ...

I loved the shower head until the washer or seal or what ever it is in the inside broke and the shower head blew off the shower arm. I need to know how to get the little ring that broke to fix it. I don't want to buy a new shower head since this one is new. Can anyone help me or tell me where to get just the ring. It hold the shower head on the arm.

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