Love the quality and stability of these planters. They look very high end. I have a 1” railing and inverted one of the screws/nuts on the brackets to hold it more snugly against the railing - see picture if you have a narrower railing. The stabilizer bars also help a lot. I’m not at all worried about them slipping. Each 36” planter holds almost 1 cu. ft. Of potting soil so plan accordingly!