If you have an old car with a cassette player you never use... then why not use it to mount a holder for your iPhone or smart phone. This holder is designed for an iPhone with a bumper or case mounted. It would properly also fit many smart phones out there. Slot for the phone is 13mm x 63mm and fits my phone perfectly. It has a slot for charger cable and air slots for the speaker and mic. Phone not included ;-)The holder for the phone is designed with 2 mm walls to be ridget. I printed with 1mm wall thickness to have the phone slot solid (2x1mm wall) and the tounge for the cassette player hollow. Printed with: 0,3 mm layer 20% infill 1 mm wall thickness