The invention comprises a first fixture group for clamping a first erecting rod, a second fixture group for clamping a second erecting rod, a fixed bolt and a compression spring, wherein the first fixture group comprises a first cylindrical portion with a first non-circular axisymmetric profile, the second fixture group comprises a second cylindrical portion sleeved with the first cylindrical portion, the second cylindrical portion comprises a second non-circular axisymmetric profile correspondingly sleeved with the first non-circular axisymmetric profile, and the first cylindrical portion axially slides relative to the second cylindrical portion to have a rotatable rotating position and a non-rotatable clamping position, the fixed bolt penetrates through the second cylindrical portion, the first cylindrical portion and the compression spring to be screwed with a nut, and the first cylindrical portion is pushed by the compression spring to move from the rotating position to the clamping position.