A variety of assemblies for coupling pieces of tubing have been proposed. Typically these assemblies include a connector body for holding the tubing, a nut threadably engaging the connector body and one or more ferrules radially compressed by the nut-connector body engagement to grasp the tubing and form a fluid tight seal. However, these assemblies have not been fully satisfactory. Especially where flexible plastic tubing is employed, current designs do not provide a strong mechanical grip on the tubing such that the tubing resists twisting and separation from the connector assembly. Many of these prior assemblies also require substantial torque to compress the ferrule and achieve a fluid tight seal.