The official name of plum screw is ISO10664 screw or inner screw, also known as star screw. The plum design is closer to 90 degrees than the hexagonal contact angle, so under the same torque, the potential destructive radial force will be much smaller. . This feature allows the screw head to be made smaller at the same torque, with the advantage of reduced space. But the disadvantage of the older head is that the smaller the inner "star", the easier it is to corrode and the plum blossoms slip and damage the head, making it more difficult to remove than conventional hex bolts.