These are terrible shelves. The back attachments are worthless. It’s impossible to get the screw in with a wall anchor close enough to make it flush against the wall. It’s particle board so if you try to get it really close it just tears through the wood. Once I got them up they were slanted and I could only put a few ounces on it or it would come off the wall. I replaced them with different ones. 
Don’t waste your money.