Most wheels used in FIRST Robotics Competition can be divided into four categories; Standard, Omni, Mecanum, and Compliant. One element to consider when choosing a wheel is the bore size, and if you will need any additional hubs to convert your wheel to the needed input or output.
Most sizes of ION wheels feature a MAXSpline bore that can fit standard 1.125in OD bearings or easily be adapted to other bores using MAXHubs. Smaller wheels feature 1/2in hex bore. Larger sizes of ION Traction, Grip, and Omni Wheels have spokes with a bolt circle of #10 clearance holes patterned outward at 1/2in pitch. They also have a 3/8in-wide nut groove that eliminates the need for a wrench when utilizing the holes on the spokes.

Wheel Basics

REV Robotics offers three types of ION wheels: ION Traction, ION Omni and ION Compliant. There are two types of ION Traction wheels available: the standard ION Traction Wheel and the ION Grip Wheel. The main focus of the traction wheels is to pull a robot (or create traction) in a forward/backwards motion.
ION Grip / ION Traction / ION Compliant wheels can easily be mounted flush when a build needs to gain load capacity or to increase traction as the cross section image above illustrates