Lightweight rods and Studio Rods.
There are actually three "standards" for rods.
Lightweight 15mm.
Studio 15mm.
Studio 19mm.
Studio 19mm and the lightweight 15mm is how the VAST majority of accessories will work.
You use Lightweight rods for scenarios where you want a smaller build but you still need something to mount lens motors too and occasionally hand held brackets.
19mm rods are able to support heavier weights, and are spaced wider apart, allowing for larger diameter lenses. Like this.

- FFD07F28-4352-45C6-AF75-33B7D62DB550.jpeg (574.14 KiB) Viewed 396 times
What's cool here about what BMD have done is they've made a SINGLE baseplate that actually does BOTH. Normally you would have two, a Lightweight baseplate and a Studio baseplate. Now you have one that can do both standards AND it's a shoulder mount too. That's a huge huge thing in my view.
JB