As the advanced robot gripper sub-system group in UBC Open Robotics Team, our goal is to develop a versatile robot manipulator for a housekeeper robot which performs tasks in everyday environments. The gripper needs to grasp objects of different shape and size and manipulate them. Simple grippers in the market are not appropriate for our application because they are not capable of adapting to the shape of different objects (unless special adapter is prepared for each specific scenario). As a result, the holding forces are limited by the object strength, and they generally rely on friction forces to lift the object. Therefore, we took inspiration from the MARS robotic hand developed in Laval University, and designed the parametric CAD model of an under-actuated robot gripper, which is characterized by having fewer actuators than degrees of freedom. When applied to mechanical fingers, the concept of under-actuation leads to self-adaptability, which is to envelope the grasped object automatically without complex control strategies. This is achieved by strategically introducing elastic elements (e.g. springs) and mechanical limits in the gripper mechanisms.