assume as nearly as possible a horizontal position without this acentricity i e if the cross pin were located precisely on the central axis 29 of the bucket the bucket theoretically because of gravity could never assume an absolutely horizontal position by way of example this acentricity or offset distance 33 typically is selected to be about 20 mils for a bucket capable of holding 38 5 ml of fluid and to be used in a rotor spinning at 27 000 rpm although preferred this offset for the pin need not be used if desired and the cross pin may be located on the bucket axis other offsets may be used according to the weight of the bucket and the angular spin rate of the rotor the hanger assembly 20 includes a hanger 34 the hanger 34 may be described as elongated and generally tubular having planar exterior surfaces 36 as is seen most clearly in fig2 such that it has a generally square or rectangular exterior configuration when viewed from the end with rounded corners 38 and a cylindrical interior 39 the hanger 34 is adapted to have a sliding fit within a receptable 40 formed in the rotor itself such that the hanger is capable of a sliding movement along its axis and or a radius of the rotor the receptacle 40 also has a square or rectangular cross section to prevent the hanger from rotating about its path of movement the rear portion 42 of the hanger is of a reduced diameter to provide a sliding fit about a shoulder screw 44 the screw has an enlarged head 46 that fits within the hanger a compression spring 48 fits over the screw and is compressed between.