When I built my own Longboard I needed to mark places to drill for the trucks, Only putting a truck on the wood wouldn't be precise enough, so I made that thing, so you line everything with the board to get the screw holes drilled correctly

 F3D file Included, mine is for a 10cm wide board, modify it to suit your needs ! 

( the actual one is made for new school, aka the longest distance possible beetwen trucks )