Abstract: A reciprocating piston used in particular in heat engines and other industrial machines comprises at least one decompression chamber delimited between the bottom of an annular groove and the inner face of the first ring housed in this groove. A split ring of small cross section is movable in this decompression chamber. Additionally the upper bead of the piston presents on its periphery projecting parts and recessed parts, the projecting parts having an initial deameter, before running-in, such that the diametrical clearance when cold, between the periphery of the bead and the bore of the cylinder in which the piston is housed, is substantially equal to half the corresponding usual clearance between conventional upper bead and cylinder.