An adaptor for use in a centrifuge bucket for evenly distributing a number of cylindrical test tubes thereacross and for maximizing the number of test tubes positionable in the bucket. The adaptor comprises a thin, flat, disc-shaped plate having a diameter approximately equal to the inside diameter of the bucket and a plurality of separate, unconnected partitions made integral with and extending normal to one side of the plate, the partitions defining a plurality of cavities for receipt of the bases of the test tubes. The partitions support substantially less than the entire circumference of each tube and have lengths which are substantially less than the lengths of the tubes. A lifting tray and handle provide means for lifting the adaptor and test tubes from the rotor bucket.