How do I "copy focused block"?

[Nerdygamer1]

In the controls option menu, there's an option for "copy focused block." The tooltip says pressing the assigned button will spawn a stack of whatever block you're looking at in your inventory. I have this bound to middle mouse button, I have cheats enabled, I have godmode enabled, yet nothing happens when I press the button.

I'm trying to figure out what blocks the devs used to build the framing of fireplaces. It's like a quarter slab, but when I try and build one, I can't get it to rotate into the corner of the empty space (even with advanced rotate on) - it just wants to stay centered on whatever face it is.

[Crater Creator]

With debug mode on (dm in console), press F3. Then you'll get debug information, including the name of the block on which you're focusing. It can be a little wonky, frequently returning a result of "air", so try looking at the block from different angles.

[Nerdygamer1]

That got me what I needed, thanks! It's a concrete 1/4 block. Now I have to figure out how to craft a concrete 1/4 block... I thought rebar would have a building option for it, but it doesn't. Wood frames and flagstone both have their respective "1/4 SCtr" blocks, but that's the block that's centered on each face. I'm almost wondering if it can't be crafted, because the wooden 1/4 block's description is "A building block from the creative menu."

Might have to justify a bit of cheaty-cheaty.

[Sinbad]

To craft the concrete shape block you will need concrete mix and craft wet concrete block in the mixer.