Panel fit and what the voltage output means
The Omron E5CC-QX3A5M-308 is a 1/16 DIN temperature controller from the E5CC series — that square 45.00mm x 45.00mm panel cutout is the standard footprint for this class, so it drops into any existing 1/16 DIN panel hole without re-cutting. The 'QX3A5M' in the order code signals a voltage pulse output for driving an external solid-state relay (SSR), plus heater fault detection built in. That means the controller itself doesn't switch the load current — it sends a DC pulse to a remote SSR, keeping the heat-generating switching off the panel face and letting you size the SSR for the actual heater amps.
Active production and sourcing reality
It ships in bulk packaging, which means you're getting the controller in a standard carton, not a retail box — fine for BOM replenishment, but if your receiving dock expects individual retail packaging for spares, flag it on the PO.
What the E5CC-QX3A5M-308 replaces and what it doesn't
The closest functional sibling is the E5CC-QX3A5M-001 — same 1/16 DIN, same voltage output for external SSR, same heater fault detection. The difference is packaging: the -001 comes in a box, this -308 ships bulk. Electrically they're identical, so if you've got a BOM line for the -001 and stock is tight, the -308 is a straight swap on the panel cutout and wiring.