The neck variable plays a key role in the dynamical processes of nuclear fusion or fission. Generally speaking, the definition for this variable is different for various parameterizations describing macroscopic nuclear shapes. In order to investigate the effects of increased neck in nuclear fusion, we extend the dumbbell parameterization by taking deformations of both the target and projectile into account. The potential energy surface (PES) with different shapes of nuclei is calculated, as well as the inertia mass and friction tensors. These calculations lay the foundation for Langevin dynamics. Analysis of the results shows that the neck variable in the proposed five-parameter dumbbell model is an unstable degree of freedom and play an important role in nuclear fusion.