Several answers suggest Wingits. Please be mindful this solution is not appropriate for sheet rock less than 1/2". I just bought some and planned on using them. After investigation....pulling off switch plates and toilet paper holder I discovered the wallboard was only 3/8" thick. Now I am trying to find some framing studs that might be used to attach the grab bars to. Studs are usually spaced at 16" on centers. Length of bars don't always make mounting them horizontally possible. I have 18" bars and have mounted them on a slant to accommodate the stud to stud dimension.
We did. Contractor said standard construction method for tile above tub and in shower provides a strong enough base for secure use of grab bars.
Concrete anchors
Yes
It really depends on what kind of wall is behind your shower, if any. I will include a picture from home depot‘s online catalog of a mount that will work with sheet rock or just the fiber glass wall. I used these mounts for a couple of decades with no problems. There are grab bars that are held in place with suction cups, much like the suction cups used to move large sheets of glass. You might consider this option if you don’t know what’s behind your wall. Once you cut or drill a hole in your shower wall, it is permanent.
3 inches
Yes, as long as you hit the studs. Believe me these grab bars are very strong.
how to unsnap escutcheon
There are enough slots and holes on the mounting plates that I've been able to get two screws into a standard wood stud. You have to be careful, and to be stronger you could angle the screws a little so they head more towards the middle of the stud, but I've been able to mount these bars well with only two screws on each end.
Maybe it's made to be angled to sit over the studs?