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.
Grab bars are designed to be mounted into two wall studs spaced 16 inches (406 mm) apart. If your studs are spaced 18 inches (457 mm) apart or follow a non-standard layout, you’ll need to anchor one side into a stud and use a wall anchor (not included with Delta® or Franklin Brass® grab bars) on the other side.
For recommended anchors, check out our options available at Lowe’s, Menards, Amazon, and Ace Hardware. Model numbers are DF549 & DF548.