Heavy-Duty Vortex includes a holder for securing accessory tube racks. Mini Vortex Mixers need retainer to secure accessory racks. 6 racks available for Multi-Tube Vortexers from 10-29mm dia. tubes.Mini Vortex Mixer foam insert holds 1 microplate. Microplate Vortex Mixers can hold up to 2. Heavy Duty Vortex Mixers can hold 8 microplates with the 4 plate holder and the stackable 4 plate holder.Magnetically attaches to either the Mini or Heavy Duty series to provide hands-free mixing of single tubes. Not for use on the Fixed Speed Mini Vortex Mixer.