An external fixator for treating a fracture of a long bone has six extension arms which are extendable out of and retractable into a main body. The six extension arms are arranged into two sets of three out opposing sides of the main body, with each set of three extension arms being able to support a fixation ring. Each extension arm is pivotable at a joint and extendable so as to allow the ring to be set at a wide range of angular positions relative to the main body. The three extension arms and the ring each define a wrap angle about the axis of the long bone being treated. The longitudinal position of each extension arm can be changed either with a coarse adjustment capability or with a fine adjustment capability, with the coarse adjustment capability being through rotation of a thumb wheel.