This measurement is called “projection” and can be found in the images on our product pages at our retailer partner websites. Generally, square shaped pulls will have wider projections for larger hands or knuckles. Here's an example for the solid bar pull.
It depends on the model. Some Delta® or Franklin Brass® grab bars feature a peened or textured finish for extra grip, while others have a smooth surface, like this decorative grab bar. If you’re looking for a grippy option, check out this Delta® 16-inch shower grab bar model.