If you own a Retroleum SmartCard V2 or V3.1 from Phil ( http://blog.retroleum.co.uk/smart-card-for-zx-spectrum/ ) you may look for a nice case.
There is one case available from Johan at https://github.com/SM7I/SmartCardv2 , but it doesn't fit to the Spectrum Plus cases and needs to be glued.
So, I designed this one from scratch so that it fits nicely on all Spectrum cases.
It works without support and both parts snap together nicely with the need of glue.
Also, I have added the STEP file and the Fusion 360 Archive so that you can adapt the case to your needs.
I used a functional variable for the 3d print precision. Look at the screenshots how to find that parameter in Fusion 360. Using 0.2mm fits nearly all printers, but something you need to increment to may be 0.3mm if your printer is not dialed in perfectly. Maybe you have to lower the value because your printer is very precise.
The author marked this model as their own original creation. Imported from Thingiverse.