These are MakeBeam 10cm prototype .STL files that have been run through "Magics 14 64bit" to remove all kinds of errors and make play nice with the majority of 3D printers throughout the world... (courtesy of Materialise)
I've included a 254mm (10") for yucks (if you print on a Dimension - wrap it with support material otherwise it will bend on you ...)

Note: as a curiosity I made a horizontal an a vertical lay/orientation - and as you would guess the horizontal is a lot stronger. If I had unlimited funds, it would be interesting to do real testing to see at which orientation (90, 60, 45, 15, 0 with rotation components also - permutations get astronomical), would be best to build for overall beam performance verses maximizing in a single plane of force (vertical lay/orientation with no side forces would win hands down, compression load only)

download and print - most important have fun !