George E. Cawthon wrote:

I don't see why you need the tabs. According to your diagram, if the
strainer is sized right it would fit in the depression. You could put a
very thin amount of plumbers putty in the depression ring and just press
the strainer into it. Cut the tabs off or just bend them flat. Or,
get a strainer that has tabs spaced to fit inside the drain pipe.

It seems very common for metal shower drain strainers to be manufactured
that way (i.e. with those little bent "tabs"). I guess they are designed
to be held in place by friction for easy removal. You may sometimes want
to remove the strainer to clear a clogged drain, for example.