As far as toys go, Legos and Knex were by far my favorites for building when I was a kid, and I did a lot of building.  I have now passed on my Legos and Knex to my kids and I still love building along with them.  A large part of my childhood was also spent outdoors running the neighborhood, building forts, and playing sports.  When it came to building life size things I had to use what was available, and in America there is nothing more available than common framing lumber.  I do not know about the rest of the world, but in the US 2x4s are used to build just about anything and scraps are abundant. 

Much like Lego using the common brick, I tried to pattern my building pieces after the two most widely used building lumber sizes:  the 2x4 stud and 4x4 post.  With those two, a person can build nearly anything.  Yes, we will ignore the very odd fact that in America a 2x4 stud is actually 1.5x3.5 inches and a 4x4 post is 3.5x3.5 inches.  My toy 2x4s are in reality 6x12mm and the posts are 12x12mm.  Real lumber is fastened together with either nails or screws which are not really an option with toys, so I went for a pin and slot interlocking system.  There are two shapes of pins:  square and round.  For situations where a joint needs to be orthogonal a square pin is used, and for times when a joint is not orthogonal or rotation is needed a round pin does the job.  The pins can be cut with scissors to any length.  I think of the length of the lumber in terms of feet with 4 slots making up one foot and 1, 2, and 3 slots making up 1/4ft, 1/2ft, and 3/4ft respectively, but you are welcome to use any numbering system you like.  Each 1/4ft, (1 slot unit) is 6mm, so that makes every foot 24mm. I created these in TinkerCAD and you can easily import and combine them to create any custom length you need.       

There are tons of trebuchet plans out there made from framing lumber so I thought I’d make a toy version to demonstrate my invention.  These milli-Lumber pieces are not only fun but, practical, and educational.  I printed mine in wood PLA to give it that wood look, but any material can be used.  A big thanks to my friend Jon Miller for doing the printing for me.  Feel free to take these and add any parts and pieces your heart desires to make your own unique creations.  Most importantly, have fun and let your imagination guide you.