A scaled-down version of the original.
Many bathroom products come with pumps to extract the bottle contents, but the tubes on the bottom of the pumps don't reach all the way to the bottom of the bottle. Thus, after the pump stops pumping, there can still be a significant amount of product still in the bottle. Rather than throw that out, people transfer the remainder into a second bottle of the same product.
These types of connectors make that transfer much easier.
The author remixed this model.
Scaled to fit a different bottle neck size. The outside diameter (not including the threads) of the neck of this bottle is 25mm. So measure the diameter between the threads to see if this is the right fit.
The original had overall XY dimensions of 60x60mm (with the big wings). I scaled this down 1/6th, to 50x50mm to fit the hand cream bottles shown. I think this is a common neck size for bathroom products. I only scaled the diameter, not the height, so the pitch of the thread is the same as the original and is a perfect fit for this bottle size.