Mazak BT40 SK40 Pull stud used in CNC machines for BT40 holders ISO standard name is MAS403 Pull studs are an important link between machine and tool. The requirements concerning accuracy, rigidity and reliability are very high. Pull studs of minor quality not only decrease the performance of the machine, they are even a safety risk. A breaking pull stud might cause severe damage on machine and workpiece and even injuries on persons. made of special steel for higher rigidity proper heat treated ,