Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Will these hold books and what is the thickest shelf it will fit over?
Document: Tried this on a white wire shelf in my closet but it does not fit. Perfect for flat particleboard bookshelves though. So I'm using it as a divider/bookend for books on my cheap bookshelf. For that purpose it works great!
I gave this a 4 star because its really not top quality, but it suited what I wanted perfectly. I had a standard closet shelf that I wanted to store Tshirts and sweaters. It fit perfectly, stays upright and keeps everything neat. It is not adjustable for shelf thickness, so do what I did and order a pair to try. I ended up reordering. I am looking for the complement for wire shelving. I think for the light use I have planned, they should hold up and not chip/rust.
Each shelf divider was very fancy and good looking, and fit well in the closet. Made my closet a lot more bearable.
One was bent a little too wide at first but was very easy to adjust by squishing it tighter- it fit the shelf great thereafter and it doesn't come off.
I have a standard size closet shelf and bought two sets of these to help organize my folded shirts and pants. While they are ok they do not fit as snugly as I would like on the shelf and sometimes wiggle around a bit.
Had no trouble putting these on the shelf in my closet. The depth allowed to fit snugly over the top and bottom of my shelf was just right. If you have a thicker board for a shelf it might not fit. My only issue is that I have tall stacks of sweaters etc and this divider is not as tall as my stacks. So far, though, none of the stacks have fallen over.
I bought these for the shelf above the hanging clothes in my bedroom closet. They fit perfectly (I had carefully looked at the size before ordering) and make it so much easier to keep my clothes stacked neatly. I am hoping that when vacation is over and I get back to my busy schedule, my closet will continue to look just as nice and organized.
I am a teacher and have several binders for each subject. Most of them are slick and were slipping around on the shelf. I got 2 pair of these and now my binders all stand neatly on the shelves and are staying right where they belong. I used them on a rattan bookcase. I was skeptical. I didn't think they would fit, but they fit perfectly with no problem. I even ordered two more pair today to replace the standard book holders on my other bookshelves. They are a little pricey; but if it keeps me organized and makes my job easier, then it's worth the investment.
The divider didn't fit any of my shelves. I opted to not return them as it would have cost more that I paid for them.
These work very nicely and look great in my closet. They fit well over the shelves. A little pricey though.
Answer: i was not impressed with these shelves.  you can go to containter store and buy them.  they fit over about and inch plus shelf.  there is a lttle wiggle room but if you force it it will break (as mine did) where its sautered together.  it should hold books but how well will depend on how the rack fits over the shelf.  hope this helps.