What it is on the FX5 backplane
The Mitsubishi FX5-SF-MU4T5 is a 4-input / 4-output expansion module for the MELSEC iQ-F series PLC platform, used to extend the I/O count of an FX5 CPU when the base rack runs short of points. It sits downstream of the CPU on the iQ-F extension bus, addressed as a slice in the project rather than as a stand-alone controller. Catalog class is PLC expansion under the iQ-F family; the module is an I/O slice, not a CPU, not a power supply, and not a motion or positioning card.
Buyer-side takeaway
For a buyer landing on this exact order code with an FX5 line to extend: the part is current, the role is a 4-in / 4-out iQ-F slice, and the right move is to quote it to order against the FX5 BOM rather than chase a non-existent cross-reference. Send the FX5-SF-MU4T5 line in on an RFQ with the host CPU model and the existing I/O map so the slice lands in the correct expansion slot.