The Maxi Mix® I (M4820-1/1E) features a soft foam rubber pad that permits vortex mixing of 1 - 4 test tubes simultaneously, depending on tube diameter. Excellent for mixing the contents of small flasks with closed tops. Convenient top-mounted push button on/off switch can be activated with either a finger or test tube. Vary vortex mixing by simply changing the pressure of the tube or flask against the foam pad. Clean, white durable plastic case is both acid and alkaline resistant. Special rubber feet prevent mixer from moving during operation. Supplied complete with one extra foam top (M4820-3), power cord and plug. The Maxi Mix Plus (M4820-2/2E) is designed with a heavy cast aluminum body to provide optimum bench-top stability. The mixer has two modes of operation: Continuous operation when you need to mix a quantity of tubes in sequence; intermittent operation is activated by touching the cup attachment with a test tube. Equipped with a single tube mixing cup for single tube mixing and a soft foam pad and mixing platform for mixing 1 - 4 test tubes simultaneously. Special rubber feet prevent mixer from moving during operation. Supplied complete with one extra foam top (M4820-3), power cord and plug.