This is a mounting plate for the Z80/Z180-based RC2014-compatible 8-bit computer SC113 modular backplane expansion board and the SC112 Powered modular backplane board by Stephen Cousins.
https://smallcomputercentral.com/sc113-modular-backplane-rc2014/
https://smallcomputercentral.com/sc112-modular-backplane-rc2014/
This plate provides a solid base and reinforced card slots support and can be used with the SC126 main board mounting plate side-by-side.
https://www.printables.com/model/632080-sc126-rc2014-mounting-plate
Intended for M3x6mm mounting screws directly into the plastic (2.9mm holes)
The author marked this model as their own original creation.