Ski boot safety binding

A heel piece of a safety binding for a ski boot, comprising a tubular binding body (1) which is connected to a sole grip (1a) and is articulated about a transverse cam (10) forming part of a stirrup piece which is linked to a pivoting plate mounted on a rail, along which rail this plate can be positioned by positioning means, the tubular binding body containing at least one spring (5) which works in compression between a piston (6) bearing upon the cam transverse and a stop (7) having a setting screw (8) for adjusting the piston bearing upon the cam, the transverse cam being formed by a cylindrical part (10) which serves as a rotation pin for the tubular binding body (1) and has a first zone comprising a substantially flat surface (11) extending parallel to an axis of said cylindrical part, with the piston (6) bearing on this flat surface when the heel piece is closed, and a second zone of the cam on which the piston bears when the heel piece is open, said second zone having at least two contact points that define a line which is other than parallel to said axis of the transverse cam, and which acts as a stop so as to limit rotational movement of the tubular binding body about the transverse cam so as to limit the tilting of the tubular binding body when the heel piece is being opened.