Compare

Which one goes
in your rack?

Start with the board. ATX needs 4U, because an ATX board's I/O edge next to a flat ATX PSU comes to 455 mm, wider than the 427 mm inside the rack. The PSU has to stand upright, and upright it needs 4U. mATX and Mini-ITX fit every height, so then you pick by cards and cooler.

By height

2U, 3U, 4U at 400 mm

	2U	3U	4U
Front panel height	88.1 mm	132.55 mm	177 mm
Motherboards	mATX, ITX	mATX, ITX	ATX, mATX, ITX
Expansion slots	4× low-profile	4× full-height	7× full-height
GPU	Low-profile only	Full-height dual-slot, 300 mm+	Full-height dual-slot, 300 mm+
Card bracket shelf	Front panel top flange, fixed	Front panel top flange, fixed	Separate, adjustable ±3.8 mm
ATX PSU	Lying flat, front-left	Lying flat, front-left	Upright, front-left
CPU cooler	≤ 72 mm	≤ 115 mm	≤ 160 mm (≤ 130 mm with middle drive)
Front drives	M.2 only	1× 3.5″ under the top plate	2× 3.5″ + 1× 2.5″ under the top plate
Top plate	—	Left half, over the PSU	Full width
Side gussets	—	Full height, to Y 205	Full height, to Y 205
Sheet parts	4 (+2 optional rails)	7 (+2 optional rails)	8 (+2 optional rails)
Steel mass at 400 mm	≈ 2.3 kg	≈ 3.4 kg	≈ 4.4 kg

By depth

	280 mm	400 mm	500 mm
Floor drives, 2U	—	2× 3.5″	3× 3.5″
Floor drives, 3U	—	2× 3.5″	3× 3.5″
Floor drives, 4U	—	1× 3.5″ + 1× 2.5″	2× 3.5″ + 1× 2.5″
Sheet area 2U / 3U / 4U	0.19 / 0.30 / 0.40 m²	0.24 / 0.35 / 0.45 m²	0.29 / 0.40 / 0.50 m²
Steel 2U / 3U / 4U	1.8 / 2.9 / 3.8 kg	2.3 / 3.4 / 4.4 kg	2.8 / 3.8 / 4.8 kg
Side rails (optional)	SR-280-L/R, 60 mm	SR-400-L/R, 60 mm	SR-500-L/R, 60 mm

For a router, a NAS head or a low-profile NIC box. Choose it when rack space is tight and a 72 mm cooler is enough.

For an mATX workstation or a GPU node with one full-height card. Choose it when you want a tower cooler without going to 4U.

For full ATX, several GPUs or HBAs, and the most drives. Choose it if you are not sure. It is also the one you can print.

Sheet metal or 3D printed

EM-CASE-R-4U-280 sheet-metal chassis, rendered from the design — Sheet metal laser-cut, folded, riveted and screwed

EM-CASE-R-4U-280-P printed PETG chassis, rendered from the design — 3D printed PETG, heat-set inserts

	Sheet metal	3D printed
Model	EM-CASE-R-4U-280 (also 400, 500)	EM-CASE-R-4U-280-P
Material	1.2 mm galvanised steel, 2 mm ears	PETG: 4 mm panel and floor, 3 mm top plate, 6 mm ears
Finish	Bare galvanised as standard, powder coat optional	Your filament colour
Parts	8 sheet parts, 2 optional rails	11 printed pieces, each fits a 256 mm bed
Made by	Laser shop + press brake	Your printer, about 45–60 h
Joining	Riveted frame; top plate and card shelf on M3 + nyloc	M3 into 56 heat-set inserts
Weight	≈ 3.8 kg steel	≈ 1.4–1.7 kg PETG (about 2 spools)
Layout	Board, I/O, slots, PSU, drives at the same coordinates	Identical: generated from the same layout
I/O shield	Clips into the 1.2 mm panel	Clips into a 1.2 mm rim recessed into the 4 mm panel
Chassis ground / EMI	Yes, through standoffs and the I/O shield	No: grounded through the PSU only
Rack load	Ears carry everything; support the rear above ~8 kg	Ear, panel and side wall in one piece; keep under ~12 kg
Heights	2U, 3U, 4U	4U