Im confused at why you think that it doesnt say anything about a 3.0 box in the instructions you posted and the image and the back plate says 4 inches, which is standard.

• Backplate: 4" Round

He said that his box is 4 inch square - not round or oct.

Has the electrician just not installed the mud ring yet?

@Seabornman @dennisgli This is the picture of the j-box. I guess it is kind of octagonal, perhaps?

(It is not mounted, just hanging there. No electricity running as yet.)

I just measured it. On the diagonal, it is 4". From side to side, it is 3.5".

Would a mud ring/ mounting bracket go on this before or after the drywall?

What concerns me is it's spec sheet below calls for a 3" junction-box @RL Relocation.

Can this box be made to work or do I need a smaller one?

https://circaskin.circalighting.com/media/pdf_uploads/TS_TOB2022PNWG.pdf

I think it can work with a mud ring like https://www.homedepot.com/p/Steel-City-4-in-Metal-Square-Mud-Ring-Case-of-25-52C312-25R/202595769 which is installed before drywall.

I agree that a mud ring should work. However, you'll still have to talk to your electrician about it. Sorry.

From your picture and measurements that looks like a standard 4 inch octagonal box. Not sure how your electrician is planning on mounting it. I don't think Seabornman's mud ring will work since it is for a 4 inch square box - I don't think those are usually used for light fixtures.

I'm still not seeing where it says that you need a 3 inch box. Are you talking about this:

• * Requires Smaller Outlet Box

I guess I'd recommend buying a sconce that uses a standard box.

Backplate: 4" Round (in the description)

So, obviously a round 4" backplate won't completely cover a 4" square box.

The box is fine; you'll adapt your way out of this one.

There is an appropriate mud ring to fit your box. Your electrician should know where to get one.

This might work if the diameter of the mounting holes in "back plate (A)" match up with it.

You'll have to get it before the drywall goes up.

RACO 737 4IN RND 1/2D PLASTER RING

This is the plastic equivalent to the plaster mud ring above. https://www.homedepot.com/p/Carlon-4-in-Blue-Nonmetallic-Round-Plaster-Mud-Ring-for-Electrical-Ceiling-Box-A471RR/100149592

Don't miss the key point mentioned by dennisgli - the metal box and this plaster ring must be installed and recessed 1/2" into the wall before the drywall goes up.

Most electricians typically use the expandable bracket on the metal box to install the box it so that its edge sticks about 1/2" farther out than the face of the stud. Then you install 1/2" drywall and it is even with the box face. In your case the best solution is to instead make the box face even with the -stud- so that when you add the 1/2' depth of the installed mud ring it will now extend the correct amount to match the drywall. Then the opening they make in the drywall will be the size of the 3" round hole in the plaster ring.

Use of plaster rings is very common, but they need to know ahead of time.

Bruce

Thank you @Bruce in Northern Virginia, @dennisgli & @Seabornman! I went to Home Depot and got the mud ring suggested which perfectly reduced the opening size down to a 3" circle. I grabbed the one specifically for the octagonal box and not the one for the square box, as they are not one size fits all, as noted above. Thought, geee, wouldn't want to have gotten home to find that I had the wrong one. Left feeling pretty pleased with myself.

Got home and realized I stupidly only bought ONE!!! That elated feeling was pretty short lived. lol