Looks to me like where you slid into the plug and a clip on opposite side to hold it in place.
I was looking through my computer, and I saw that there is a place to put HDD storage. As I would like to add some storage, now that I know that there is space, I cant find the plug for a HDD to plug into. There is this weird rubber thing on the end of the space, and I wonder if it is the plug. Does anyone know what the weird black rubber thing is, and if I can put a HDD into my device? Thanks.
P.S. Here is a picture for reference: Picture

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