The ST 28 is a set of expanding lathe mandrels. There are 8 pieces in the set which rests in a nice wood stand and includes allen wrenches for the various expansion bolts. At times you may need to turn a part in the lathe that has in internal hole too small for the chuck jaws. Use these mandrels to grip the part then grip the mandrel in your chuck. The eight mandrels cover a range of hole diameters from 1/4" to 1 -1/4". Works on metric parts as well from 6MM to 31MM.