Three clear glass files of medium, fine and super fine grit. Their transparency allows for the observation of the sanded surface - as it's being sanded (mind-blown emoticon).  For best results start with medium, and work your way to superfine (similar to the progression of my significant others).  For the cleanest finish, use the Infini Softback Stick 4000 afterwards. Clean/maintain with warm water and rag.  

Approximately 90mm X 8mm X 3mm