Thin Lie algebras are infinite-dimensional graded Lie algebras L = ∞ i=1 , with dim(L 1 ) = 2 and satisfying a covering property: for each i, each nonzero z ∈ L i satisfies [zL 1 ] = L i+1 . It follows that each homogeneous components L i is either one-or two-dimensional, and in the latter case is called a diamond. Hence L 1 is a diamond, and if there are no other diamonds then L is a graded Lie algebra of maximal class.We present simpler proofs of some fundamental facts on graded Lie algebras of maximal class, and on thin Lie algebras, based on a uniform method. Among else, we determine the possible values for the most fundamental parameter of such algebras, which is the dimension of their largest metabelian quotient.