of the adaptor 30 referring to fig2 and 4 side edges 72 74 of each shell piece 60 a 60 b form mating surfaces that abut against and mate with one another to form a joint 76 fastener holes 78 are formed along the lengths of the side edges 72 74 that allow passage of fasteners 80 such as bolts that removably secure the shell pieces 60 a 60 b to one another surrounding the adaptor 30 the interior surface 64 of each shell piece 60 a 60 b is also formed with a friction enhancement section 82 best seen in fig2 and 3 that is configured to enhance frictional engagement between the pull head 32 and the exterior surface 44 of the adaptor 30 the friction enhancement section 82 can have any configuration that is suitable for achieving this function in the illustrated example the friction enhancement section 82 can be formed by teeth knurling rubber pads or other friction enhancement features that engage with the exterior surface 44 of the adaptor 40 the exterior surface 44 opposite the friction enhancement section 82 can be substantially smooth or the exterior surface 44 can be provided with friction enhancement features that engage with the friction enhancement features of the friction enhancement section 82 the friction enhancement features can be integrally formed with the interior surface 64 of each shell piece 60 a 60 b or the friction enhancement features can be formed by a separate layer of material that is fixed to the interior surface 64 or simply disposed between the interior surface 64 and the exterior surface 44 in addition in the illustrated example the friction enhancement section 82 extends from one side edge 72 to the other side edge.