These small (30mm, 40mm, 50mm diameter) are perfect for a bubble catch routine.  Imagine blowing a bubble using a small bubble wand from a pot of kids bubbles and then reaching out and grabbing it from the air making the bubble solid in the process. A great effect for kids or adults and these clear acrylic balls are perfect sizes for the effect.  Also, good for adding to your manipulation as the clear acrylic creates some great optics under bright lighting.