Abstract: The present invention relates to an inventive non-elastomeric thermoplastic cap assembly that may be secured on an end of a generally cylindrical body at room temperatures. The cap is a deformable tubular sheath having an interior surface, an exterior surface, a first open end for receiving the end of the cylindrical body, and a second end which is at least partially closed to inhibit passage of the cylindrical body through the second end. The sheath has a gripping region adjacent the first open end to engage the exterior surface of the cylindrical body. The gripping region may include at least one ridge on the interior surface of the tubular sheath. The sheath also has a transition region adjacent the second end of the sheath, which helps the sheath provide a controlled and predictable amount of retention force over a wide range of component tolerances.