You can increase or decrease the clamp tightness by adjusting the screws on the clamp mechanism:
Loosen the two outside screws (1) at least 3 full rotations with a No.1 Phillips Screwdriver
To increase the clamp tightness, rotate the centre screw (2) with a No.1 Phillips Screwdriver 1/8th of a rotation clockwise.
To reduce the clamp tightness, rotate the centre screw with a No.1 Phillips Screwdriver 1/8th of a rotation counter-clockwise.
Assemble the Left and Right shafts together and check the tightness of the clamp by twisting the two shafts in opposite directions. If more clamping force is required, repeat the steps above until the desired tightness is achieved. If the clamp-lever requires excessive force to operate, then consider reducing the tightness of the clamp.