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Guide

How to read a Siemens part number (MLFB) and find the right variant

How Siemens order numbers (MLFB) are structured, why one digit changes the variant, and how to confirm the exact part before you buy.

  • 5 min read
  • Updated

The three parts of an order number

Order numbers such as 6ES7 214-1AG40-0XB0 are written in blocks. Treat the blocks as follows:

  • First block (for example 6ES7): the product family prefix.
  • Middle block (for example 214-1AG40): identifies the specific device and its main features, such as supply and output type.
  • Last block (for example 0XB0): marks the version or functional variant, and can include a product release.

Why the full number matters

A single character can change the voltage, the output type, the memory or the firmware generation. Ordering by the family or the first block alone can give you a part that does not fit or is not compatible with your programming software version.

How to confirm a part

  1. Copy the order number exactly from the nameplate of the installed unit.
  2. Check the product version and firmware on the label, because they affect software compatibility.
  3. Compare it with the datasheet from the manufacturer.
  4. If the part is discontinued, ask for the current successor and check whether its mounting, terminals and software are the same.

Typical mistakes

  • Ignoring the last block and receiving a different variant.
  • Mixing similar families that look alike but use different bus connectors.
  • Not checking the programming software and firmware version.

Frequently asked questions

What does MLFB stand for?

MLFB is the German abbreviation Siemens uses for its machine-readable product designation, which is the order number printed on the device.

Are two order numbers that differ by one character interchangeable?

Not necessarily. Different characters can mean a different supply voltage, output type or generation, so confirm against the datasheet.

Where do I find the order number on a Siemens device?

It is printed on the front or side label of the device, usually next to the product version and the serial number.

This guide is general engineering guidance. Always confirm part-specific details, ratings and compatibility against the manufacturer’s datasheet. We confirm price, stock and specifications for the exact part in a written quotation.