Ears less adjustable for 3.5" deep metal boxes vs. 2.75" deep boxes

Question

I have two single-gang metal boxes: one that's 3 1/2" deep, and another that's 2 3/4"-deep. The smaller box has the ability to adjust the depth of the ears more than half an inch. But the larger box can only adjust a small fraction of an inch. Is it a code requirement that larger boxes' ears cannot be as adjustable as smaller boxes? If not, are there any 3.5" single-gang metal boxes with widely-adjustable ears like the small one pictured below?

I ask because I need a box that can accommodate a receptacle (2 conductor equivalent), ground wires (1 conductor), and can feed another receptacle (2 x 2 = 4 conductors), for a total of 7 conductors. According to NEC 314.16(A) box size table for metallic boxes, I'll need a 3.5" box to do that. My jurisdiction adopts this section of the NEC without amendment.

But I'd been assuming that the easiest installation would be to screw the ears to the strip of lath above and below the cutout hole for the box. If I do that, then I'd need to move the box forward a half-inch or so, and those adjustable ears seem like an easy way to to do that, without the hassle of an extension ring.

Does a deep box with widely adjustable ears exist? If not, then what's another way to do this install? Should I find another way to anchor to the wall that doesn't require screwing into the lath? Should I use an extension ring? Something else?

Answer 1

There is more than one way to mount a metal box. If you can mount it to a stud then you can use something like this RACO box from Home Depot:

This particular one is designed for 1/2" setback (e.g., 1/2" drywall) but there are plenty of other varieties out there.

Plus, as noted in a comment by red_menace Those ears can also be flipped around.

While minimum size is determined by NEC box fill rules, beyond that the dimensions, available configurations, etc. are determined more by supply and demand and constraints by UL or ETL for listing products. A steel box can be made in pretty much any shape and size and provide good protection from fire, plenty of knockouts (because you want to go in the top and someone else wants to go in the bottom, etc.) and, I suspect new varieties developed faster and easier than with plastic because plastic requires a mold for each shape.