The wheels are 4.5" in diameter and about 1 1/8" thick. There are two wheels included and they are modified to fit a splined servo shaft such as the Hitec standard servos. It includes 2 long screws for mounting the wheels on the servo shaft.
These are 6" inch diameter Mecanum wheels with custom shafts, lock collars, and bearings.
1/4" Hex Size, 2" Length, 4-40 Thread Size