How to make sure it will connect properly after 3D printing

Hi !

I joined my project as a zip here.

I have those 3 parts ( one is twice in the assembly ) , I sent those file to a company to 3d print it but the piece don't fit together.

Probably because of the precision of the printer. But the major issue is that all my piece are fitting with each other exactly.

How can I add some wiggle room between the piece ?

SolidworksParts And Features