Most tempered glass shelves for the Shower are 10" x 10", or bigger. I think this is too big. You can hit your head on the shelf. My daughter hit her head on our 10 x 10 ceramic shelf and broke it. One of these days I'll fix that.
But tempering plants around here can't make 8x8" shelves. So we ordered some from over seas and we're selling them for less than the wholesale price.
They are 3/8" Thick - 8" x 8" Quarter Round.

We include anchors and stainless flat head machine screws, when you order the shelf with brackets.
Provisions for three screws, only one screw is required in each bracket.
Your choice of brushed nickel or chrome frinish.