The 2x4. Its the basic piece of modern stick frame construction. But it is not actually 2" by 4". Many of us know this, but do we know why the size has changed but the name stayed the same. Moreover how did anyone even start with those dimensions. This single piece of lumber is a representation of all the changes that have occured in the building trades and the optimization of forestry, economics, and manufacturiung. Its not a measure but a convergence of optimization.