On several pages of the Atlantic Code , in manuscript C and in the codes Madrid Leonardo has left testimony of his interest in the study of pulleys, simple and complex, and other systems lifting weights, then systems is very popular on construction sites is within foundries. Of particular interest seems the attention it devotes to Leonardo behaviour of ropes used in the operation thimbles devices: that in order to identify the forces at stake in the various positions that the ropes could be compared to individual blocks and between the rope and individual cavities where they were housed. The study of the conditions of balance between weight lifting and strength connecting rod was probably aimed also to understanding the forces of friction involved in such mechanisms. Leonardo show that they reached a mature understanding of laws governing the operation of pulleys and sizes and benefits they can offer in the transmission of movement and especially to facilitate the lifting of heavy loads. Leonardo, however, that does not consider the effect of considerable friction, says that in this paranco, composed of 33 pulleys, of which 17 fixed and 16 mobile, 1 pound of weight pareggerà a counterweight to 33 pounds. C. 1497. Code of Madrid