I realized that too late on Zalot's server lol. Not that he didn't realize either, and he practically used them everywhere :L
It's called a beveled brick. It's private. Very few people have the add-on. It's not good to build with because it was never fully vectored (or something, I can't remember the exact problem.) It also leaves small cracks between bricks, so really if that's all you used between walls, your build would have spots where people could see outside, ruining the effect.