It is a plastic piece. The raw materials that make up the harpoon are very important; it should not be too hard and rigid that it becomes brittle, and also not too soft that it stretches. The threading grooves on the side of the spring should be designed in such a way that the winding direction of it is the same as the spring. The design of the harpoon’s arrow should be such that after passing through the cam hole of the spring, it returns to its original state and prevents the spring from coming out of the cam hole, which is a very important point.