A lot of people have been asking how. It’s very simply done with a tool called Precision Alignment. Don’t be deterred by this tool’s seeming overcomplexity, it is extremely powerful for building, I can’t even grasp most of it.
Ok, so to start off, download the set of tools with PA in it, install it, or just whip it out if the server already has it.
Place a prop in the center of everything, this will be your “Plane”.
Place your props
Then, take your PA tool, and select Plane Hitpos+Hitnormal, leave everything else alone
Then click the side of the prop on the side you want to mirror the props to (remember that it mirrors from the side of the prop you select, not the center of your plane)
Then, with your PA tool out, press R and go to the “Rotation Functions” tab and press “mirror across plane” and click “plane 1” from the left hand plane selection table.
Now RIGHT CLICK one prop (it can only do one at a time at the moment) to select it
Now press R with your PA tool, and hold your SHIFT key and click “rotate entity”.
Now repeat the process of right clicking a prop, pressing R, and shift clicking “rotate entity” for each prop.
voila! that’s it.