I'm building 42082 and there are 4 of these but 3 unique numbers in the tops.

  • 20X8 on two
  • 29X8 on one
  • 35X8 on another

I'm guessing they are serial numbers from machines that made them but I wondered if someone had a better idea.

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1 Answer 1


First two digits represent week of production followed by a year.

20X8 - 20th week of 2018.

These codes used for quality control. LEGO Customer Service may ask you to provide this number if there were an issue with a set or particular part.

Similar code exist on box seals too.

  • 1
    Why “X8” instead of “18”? What do other years/decades use?
    – KRyan
    Mar 23, 2020 at 3:44
  • This is something unknown, probably has some company internal meaning. For example you can find "S" on boxes, "K" on some other parts. I have an old motor base from set of year 2009. It has "J8" for 2008 production year.
    – Alex
    Mar 23, 2020 at 5:54
  • 1
    If they're using multiple letter codes/year they presumably refer to different production lines, or production runs. Mar 23, 2020 at 13:46

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