This is my hardhat bottle opener with keyring.
There is a 10 EuroCent coin inside the model. This coin is placed inside while printing. The simpelest way of doing this is by pausing the print at layer 18 when printing with 0.2mm layerheight. You can just use my 3mf file, the pause and appropriate setings are used in there.
I also recommend printing with a higher infil % for more strenght.

Do NOT use supports!!

Hope you like it.
Cheers