Hello!
First, I want to ask you why you are here? There are so many chains that actually look like chains, but if you want to stay, this is a simple chain link that I made in Fusion 360, and arranged in blender. Unfortunately, when it was scaled down, its "features" were lost, and hidden inside the other parts of it, so it just looks like a rectangle. To print it, you'll need to have supports enabled everywhere, since without them, the model will not print. I hope you enjoy!