Abstract: A car body frame straightening apparatus consisting of a frame jig and a rim clamp having an adjustable attachment to the jig frame and comprising of a pair of jaws clamping to the body rim. One jaw (3) of the rim clamp is permanently fixed to a body piece (5) of the rim clamp (2) while the other, an adjustable clamp (4), is clampable by means of an eccentric clamping member (6) against the other jaw (2) in such a way that the rim clamp is clamped by virtue of an other set of eccentric elements (7, 8), which exert a clamping effect on the jig frame 1, to attach to the beam frame.