Disclosed is a clamp mechanism mountable to a coupling device having a tow ball supported by a tow ball neck. The clamp mechanism comprises a ball retainer having a ball support surface contactable at least to a first area of the tow ball located opposite to the tow ball neck and at least two clamp members which are distributed about a center axis of the ball support surface. Each of the clamp members is movably arranged with respect to the ball retainer and has a ball clamping surface contactable at least to a second area of the tow ball located on the side of said tow ball neck. The clamp mechanism further comprises a tensioning member arranged movably along the direction of the center axis with respect to the ball retainer and interacting with each of the clamp members such that by applying a force to the tensioning member, a clamping force acting between the ball support surface and the ball clamping surfaces to the tow ball is achievable.
