This is a plane rib for someone who wants to build model planes. this is an optimized airfoil for slow flight. it has holes in it to reduce weight and it is very structually strong. the square in the middle is for the spar, It is supposed to be 1/4 by 1/4inches when the file is 5.66 inches long. It can easily be printed at 8% infill with PLA plastic and still withstand up to 10 pounds of compression force.