Stackable roller carriage having swingably mounted wheels

A roller carriage comprising:

• a bottom frame having an upper and a lower surface, said bottom frame comprising a plurality of rotatable wheels disposed on said lower surface, at least one of said wheels being swingable about a substantially vertical swivel axis that does not intersect an axis of rotation of said at least one wheel, and
• retention means disposed on said upper surface, said retention means being adapted to retain at least one swingable wheel of an overlying roller carriage, said retention means comprising a support face adapted to support the at least one swingable wheel of the overlying roller carriage at a support point said support point being positioned on a circular arc concentric with a swivel axis of the at least one swingable wheel of the overlying roller carriage, said retention means further comprising an outer engagement area extending at least partly around the swivel axis of the at least one swingable wheel of the overlying roller carriage outside said circular arc, and an inner engagement area disposed inside said circular arc,
• wherein said outer and inner engagement areas cooperate to restrict a rolling movement of the at least one swingable wheel of the overlying roller carriage in a direction transversely to an axis of rotation of the of the at least one swingable wheel of the overlying roller carriage,
• at least one of said inner and outer engagement areas is provided with at least one projection adapted to engage the at least one swingable wheel of the overlying roller carriage, said projection being adapted to absorb forces in parallel with the axis of rotation of the at least one swingable wheel of the overlying roller carriage at a radial distance from said support point such that a swing of the at least one swingable wheel of the overlying roller carriage about the support point on the support face is essentially prevented for substantially any angular orientation of the wheel on said support point with respect to said at least one projection, and
• all of said at least one projection that are provided on said inner engagement areas are inside said circular arc, and all of said at least one projection that are provided on said outer engagement area are outside said circular arc.