The present invention relates to a coupling system for fitting and attaching of a removable internal basket for a washing machine. The washing machine comprises a removable washing compartment configured to be mounted in the washing machine. The washing machine includes at least one convex protrusion or at least one concave groove across a portion of an inner side surface, and the removable washing compartment includes the other of at least one convex protrusion or at least one concave groove across a portion of an outer side surface. The balancing device includes a smooth surface portion across a portion of the inner side wall and the removable washing compartment includes a complimentary smooth surface portion across a portion of an outer side surface. When the removable washing compartment is mounted in the washing machine, the smooth surface portion on the inner side wall aligns with the smooth surface portion on the outer surface of the removable washing compartment and the at least one convex protrusion nests with the at least one concave groove such that the surface of the convex protrusion contacts the surface of the concave groove.