As picture show,all arduino mounting holes are 3.2mm-about 0.125"-in diameter.they will accomodate M3-0.5 or UNC 4-40 screws and standoffs.so if i want to fasten the pcb with a plastic box or other case?
Step 1: For Test Only
if u want test arduino,u don't need to fasten it to any box,u can stick it to any surface with a spacer or standoff.
spacer like picture can do this,this spacer is with 3m glue.so the board can be glued to any surface of any object.
3.2mm hole dia link:http://www.ebay.com/itm/301532630354
4mm hole dia link:http://www.ebay.com/itm/301532642226