This is a simple sleeve case for bluepill stm32F103 mini dev kit. There is available
source on-shape url so you can edit if you like.

The bluepill, at least in my experience, comes in version with 1.2mm and 1.6mm pcb so 2 different STL's are available. You can easily create any pcb thickness you like, just edit the variable (only one available) in the source and export new stl.

my own build

Doesn't Matter

No

0.3

you can print this from 0.1mm till 0.35mm layer height and it will work. thinner the layer better the letters on the back come out but I personally print this between 0.3 and 0.35mm, 70mm/sec to get them to print faster as I don't care too much about how it looks as long as it performs the required task. I printed these in ABS but any material should work as long as it's non-conductive.

I print this with brim, so it gets better adhesion to bed since it's small area touching the bed and a tall print and then I leave the brim that closes the "rails" so on one side the slider is kinda closed.. anyhow printing without brim works too.

I print at least 2 of then in the same time to solve the heat accumulation problem