A set of 48mm LEGO NXT plastic omnidirectional wheel servo motor  omni wheels features:

The 48mm Omni wheel is a robust, Mindstorm NXT compatible omni wheel which is usually used in industrial market. It is mounted in a fixed position which is

 capable of 360 degree movement and rotation. Durable construction and unlimited maneuverability make this omni wheel ideal for tough environments and industrial applications.

The 48mm Omni directional wheel is engineered for both floor and inverted applications such as manual and powered conveyor transfer systems, feed rails, 

workstation turntables, robot wheels and so on. It comes with an NXT compatible hub and an Axle Centre hub for the Arduino motors.

Key Features:

360 degree manoeuvrability

Simple & stable mounting options

Robust and durable construction

Fits other Arduino motors with the hub included

Easier directional control and tracking

Low Maintenance

Specifications:

Number of wheels:3

Body & Roller Color: Black/Gray

Wheel Diameter: 48mm

Roller Diameter: 13mm

Body Material: Nylon

Roller Material: Nylon+PE

Load Capacity: 2 kg

Net weight: 39g

Compatible Hubs:

1. If the wheel is used to be connected with LEGO and servo motor, we provide free accessorie of a plastic cross axle and an axle center hub, The Cross axle is to be 

connected with LEGO NXT, and the axle center hub is to be connected with servo motor.

2. If the wheel is used to be connected with DC Motor, you can use following hubs:

4mm Aluminum Hub 18013

A set of 48mm LEGO NXT plastic omnidirectional wheel servo motor omni wheels pictures as below:

What are the advantages and disadvantages of the Omni wheel?

The advantages of the Mecanum wheel and the omnidirectional wheel are flexibility and convenience, and the disadvantage is expensive. The omnidirectional wheel, as the name suggests,

 can move in any direction, at any angle, and in any direction. mecanum wheel these rollers having an axis of rotation at 45° to the plane parallel to the axis of rotation of the wheel.