Okay, sorry, it just felt like it, because you kind of seem to be getting stuck on the one idea of the terrain? My end goal is just to align parts to other parts in my building system.
The use of mouse.TargetSurface was just one example of how to achieve this for specific surface types.
You can use the CFrame property of the parts. The CFrame property represents the position and orientation of a part in 3D space. By setting the CFrame property of a part to match the CFrame of another part, you can align the two parts x
But my goal isn’t to make them in the same position, my goal is to make it FLUSH against the other part, no matter the rotation of the part being placed.
You can use the hit.Normal vector to calculate the correct position and orientation of the new part.