Similar to this question I am interested in combining Duplo Lego with Mega Bloks. I want to have full compatibility, i.e. being able to put Duplo on top of Mega Bloks, which requires some type of adapter.

I am looking for BUYABLE adapter pieces (not self-made via 3dprinter or such).

Does anyone know a source?

I found that Lego has a (discontinued) system called "Lego Primo" with similar round studs. It does have adapter blocks for Duplo (marked with red rectangle):

enter image description here

Can anyone confirm that these do / do not fit the Mega Bloks studs?

Although they are discontinued, they can still be bought used. So if they fit it would be an option for me.

  1. There is an unconventional type of adapter being sold on Ebay (seems to be just a single offer, used):

enter image description here

Has anyone ever seen these somehwere else? Maybe even in real life? They do not look 3d-printed, they look injection molded (like Lego and Mega Bloks). So there might be someone producing them (or having produced them) commercially...

  • 1
    I've linked to the eBay item your picture comes from, in order to let others see the whole listing with all images. Note though that the listing explicitly mentions how "They are extremely hard to find." I can easily imagine someone having set up an injection molding line for these parts, and only producing a handful of them before getting hit by C&D letters from both TLG and Mattel - thus limiting the availability of these parts severely.
    – zovits
    Sep 7, 2022 at 13:21
  • 1
    I have several of the second (white) adapter you show in the photo, from my original 1990s Mega Bloks sets. I have the original Ritvik Mega Bloks (the only size now sold) as well as a Ritvik Mega Bloks set that is almost identical to Duplo blocks (sold in the early 90s, mine are marked 1992), with the white adapters made by Ritvik.
    – Kara
    Feb 19 at 18:48

1 Answer 1


Primo and Mega Bloks are not compatible.

The Primo piece loosely fits on a Mega Blok piece:

Primo and Mega Bloks

But the Mega Blok piece does not fit on the Primo stud.

Primo and Mega Bloks

As for the adapters in your second photo, I have seen them many times in used toy collections I've bought; unfortunately, I don't think I've ever seen them new in the package to give you a specific reference on how to buy them. But I've always assumed they were an actual Mega Brands product.

I have a 2x2 (or 1x1) and 2x4 (or 1x2) in front of me. The smaller says 430 and © 1988. The larger says 439 and PAT PEND and © 1988 and (tellingly) Ritvik. (Ritvik was the maker of Mega Bloks.)

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