i've made my first model in sketchup and i want to print it. the model has a moving parts that needs to slide. my question is do i have to build a margin between the two parts and if yes how big does it have to be in milimeters? i've addaded a picture to describe what i mean, i hope its clear.

also curious with screw holes, if i have a 4 milimeter screw and i make the screw hole 4mm wide will the screw fit? and how many parts does a circle have to have to appear round enough for screws to fit?