Handcuffs, because who doesn't like playing with handcuffs. It a simple model to assemble using CA or other compatible glue. I've only printed this model in PLA but any stiff filament should works fine. It prints with the default 0.2mm profile with auto tree supports and auto brim turned on and infill raised to 30% for extra stiffness. The brim is needed for the keys which prints on it's tip and the supports are needed for the chain which prints in place. The profile was saved to the project so it should just open with these settings.
There is an assembly instruction PDF and a zip file with the raw files in .STEP, .STL, generic .3MF and the instructions.