The needle is a square needle and the needle rubber core is an interference fit. The retention force of the needle depends on the friction force of the plastic against the square needle. Because the plastic and the square needle are material characteristics (thermal expansion and cold contraction), the retention force of the needle becomes smaller after too high temperature. Now we need to increase the friction force. First, we need to hit K point at the square needle to increase the resistance force. Second, we need to use anti fool Hardware needle.