Rigidly attached sheaves 1 and 4 rotate about axis B of the block. Sheave 2 rotates about axis D of hook 6 on which load 5 hangs at point C. Endless flexible link (chain) 3 runs over sheaves 1, 2 and 4. Load 5 is hoisted by pulling on the loose loop a of the chain in the direction of the arrow. The mechanical advantage is M.A.=(2*d₁)/(d₁-d₄) where d₁ and d₄ are the diameters of sheaves 1 and 4.
$3562$CFL,MH$