This is a cover/faceplate for the Macintosh Quadra 700 NuBus slots. My Q700 didn't come with any and I haven't been able to find any original ones, so I came up with this.
I haven't tried it on other Mac models, but it should work if the design is the same as the Quadra 700.
I recommend PETG rather than PLA, since PLA is brittle and the tab will break off easily.
The author marked this model as their own original creation.