Omni-directional wheels in the smallest diameter offered by any common FIRST Robotics Competition or FIRST Tech Challenge supplier.
These 50 mm / 2 inch omni wheels features two different durometers:
Soft 35A rollers for high traction
They also have a standard 14 mm Hex Bore, letting you choose between 3 different bores:
0.375 in. Hex - includes 14 mm Hex to 3/8 in. Hex Adapter (am-3905)
0.5 in. Hex - includes 14 mm Hex to 1/2 in. Hex Adapter (am-3904)
14 mm Hex - no adapters included
 
Stack several of these wheels on a shaft to craft an unstoppable intake system for your robot that can be used to center game pieces.