I have a slightly more nuanced answer. There are specialized shell holders that are a couple of .001's off nominal in order to help you adjust your shoulder without adjusting your die. I think Redding sells them in a set with progressive widths. And then there are the "normal" ones that come in one size from various manufacturers (Lyman, Lee, Redding, etc.). There may be slight variations between the thickness of shellholders from different companies. They will all fit your press, and in that sense are interchangeable. But it is more a "pick one and stick with it" kind of interchangeable, rather than "have a bunch in the drawer and choose one at random" kind of interchangeable if you know what I mean.