Unfortunately I have no idea. However, make sure the installer knows what they are doing when they install the bar, especially since the anchor heads are not covered like they are in the majority of the grab bars. I would never purchase a grab bar with the holes exposed again! However, from what I do know, first a special drill bit is required when anchoring in marble or tile, which Home Depot sells.. An ordinary drill bit will not do. I purchased my anchors in Home Depot. The sales person was extremely knowledgable about what type of anchors are required, as well as what size would be required because of the thickness of the area the bar is attached to and the size of the holes in the grab bar.