Install a grab bar in a bathtub by locating the wall studs, marking the location of the screws and predrilling the holes for the screws. Use the screws to attach the mounting hardware to the wall, and then attach the grab bar to the hardware.
Apply a piece of painter's tape along the approximate location of the grab bar. Use a stud finder to locate the studs and mark their location on the tape. Use a ceramic tile and glass drill bit to make an opening through the tile for the screw. You should be able to place two of the screws into the stud, but the third screw for each bracket requires a plastic anchor. Insert a screwdriver bit into the drill motor to drive the mounting hardware screws to the stud or anchor.
Choose screws that are a minimum of 1 1/2 inches longer than the thickness of the wallboard. Putting two screws in the stud provides enough strength to support a 250-pound person and prevent him from falling. Depending on the arrangement of the bathroom and the needs of the person using the tub, it may be necessary to install more than one grab bar. Horizontal grab bars provide stability when standing and vertical bars help the user to lower himself into the tub.