mirrormountingscrewswalls
I ordered a 50-pound mirror from Greece that is supposed to be wall-mounted. It came with no instructions and these things.
There are holes on the top left and top right corners of the mirror that look like this.
Presumably, the screwy part goes into a stud into the wall, but what are the black things for? Also why are the holes in the mirror so much bigger than the screwL
At Home Depot (or Lowes) you should be able to find these Spring Loaded Mirror Mounting Clips made specially for hanging a mirror. They are no where near as big as a j channel and the top two have a small spring inside of them so they kind of grasp the mirror (and snugly fit on the glass).
You put the two without the springs in the bottom and the mirror just sits in them. Two more (with the springs) added to the top prevent the mirror from falling forward. Of course it would be best if you can get them into a beam in your wall. And you will barely notice the clips on the mirror once it is in place.
This turned up a few sources --> Googling "Mirror Screw Covers"
And at least one place calls these "grommets with covers" --> CRL Mirror Grommets
Best Answer
The black things are wall anchors in case you are not screwing into solid wood, but plasterboard (or holes drilled in concrete.)
The hanger holes are large because the entire end of the "L" goes into the hole, and then the mirror drops down so the "L" holds it until it's lifted up again.
Hopefully obvious that the end of "L" should point up.