Housing for the MBC2 single board computer.

In the picture only the bottom half case with the mbc2 on top.
The top half of the case should be screwed onto this.

Room for 2 extender cards (eg USB and SD card).
Easily to adjust for your own cards if they have different sizes.

Some wedges available to fix the extender cards.

Creality

Ender-3 S1 Pro

No

No