This is a Lego Duplo compatible 2x4 Block, which can be printed without support.
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![[Updated] Duplo compatible building block 2x4 - no support required 3D model preview](https://media.printables.com/media/prints/40100/images/396470_8dd32ff6-0f98-442f-bdc1-2c9fefd11cd1/duplo_2x4-v3.png)