Clamp assembly for an external fixation system

An external bone fixation system for clamping bone pins and a connecting element is provided. The system includes a jaw and an upper element for retaining bone pins therebetween, a middle element, and a lower element, with the elements being disposed about a common axis. The upper element swivels relative to the middle element, and the lower element rotates relative to the middle element. A borehole extending through the lower element permits demountable attachment of the device to the connecting element, as well as rotation thereabout. Opposing surfaces of at least two of the elements are positively engageable. The upper, middle, and lower elements are coupled by a common fastener disposed along the common axis, while the jaw and upper element are coupled by at least one fastener that is not disposed on the common axis. A single fastener can be used to arrest two or three degrees of freedom of movement.