Norm Dion wrote:
I'm getting ready to install a safety grab bar on the wall of my shower,
which is lined with ceramic tile.
The house dates to the early 1960's. What am I likely to be drilling through
between the tile and the wall studs?

You should be hitting the studs or you will be installing a towel rack,
not a safety grab bar. Some people will tell you that toggle bolts or
some such will be adequate, but you'll be compromising safety that way.
The only time I would use toggle bolts would be on one of the L-shaped
grab bars that wrapped a corner or had a vertical and horizontal leg
and you couldn't hit a stud every time.

I'm not sure why manufacturers insist on making 18" grab bars when
studs are on 16" centers. Pretty silly.

R