TETRIX MAX Omni Wheel, 3 inch Omni Wheel with 10 Rollers, Robotics Building Elements, Spare Parts for Robotics and Vehicles, Package of 2

You do receive two of what's shown in the picture, but you may not know that both must be connected to get one usable omnidirectional wheel. You'll end up spending $100 for a full set of four wheels, and they work, look and feel very cheap.

I wish it came with more information on the other mounting mechanisms (not that I'm going to use them anyway). It's also misleading, you get two of what's in the picture, and if you want a smooth omniwheel, you need to bolt both of them together. Despite all that, it's probably the best small omniwheel you can buy in this weight/size