Siemens SIMATIC order numbers — officially called MLFB numbers — look like a wall of random digits at first glance. They’re not. Once you know the general structure, a string like 6ES7 314-6EH04-0AB0 tells you a lot before you even look up the datasheet. Here’s the practical breakdown.
The prefix tells you the product family
The first block (6ES7, 6AV, 6GK, 6EP, and so on) identifies which Siemens product line you’re looking at:
- 6ES7 — SIMATIC S7 controllers (CPUs, I/O modules, communication processors)
- 6AV — SIMATIC HMI panels and operator interfaces
- 6GK — SIMATIC NET networking hardware (SCALANCE switches, PROFIBUS/PROFINET components)
- 6EP — SITOP power supplies
If a listing’s prefix doesn’t match the product category it’s advertised under, that’s worth double-checking before you buy.
The next digits tell you the module type
Within a family, the following numbers narrow it down further. In the S7-300 range, for example, 31x generally indicates a CPU, 32x indicates digital I/O modules, and 33x indicates analog I/O — so 6ES7 314-6EH04-0AB0 is a CPU, while 6ES7 321-1BH02-0AA0 is a digital input module. This pattern is consistent enough to be a useful sanity check, though Siemens no longer publishes a full public decoder, so treat it as a strong hint rather than a guarantee.
The suffix is a version, not a variant
The trailing block (like -0AB0) generally encodes hardware and firmware revision. This is the part people skip when comparing parts, and it’s the part that actually matters for compatibility — a -0AB0 and a -0AB2 of the “same” module can differ in firmware requirements or supported features, even though the rest of the number matches. If you’re sourcing a replacement for an existing system, match this suffix as closely as possible, not just the base part number.
Why this matters when buying used
Two units that look identical in a photo can carry different suffixes, and the difference isn’t always cosmetic. When we list Siemens hardware, we always show the complete order number exactly as it appears on the nameplate — not a rounded-off version — specifically so you can compare it against what your system needs before you commit. Browse our current Siemens and industrial automation inventory, or if you’re not sure whether a specific MLFB is right for your setup, our sourcing team can help you confirm it first.