You need to look at the following things before selecting the castor Load Carrying Capacity: The load that you need each castor to bear Floor type: This will help you in selecting the right wheel material in terms of durability. The height required: You should know the distance between the floor and the application (e.g., trolley) to help you decide on the wheel diameter. Top Fixture: Fitting the castor onto the application can be done via a top plate, a kingpin, a threaded pin, a solid plug, or just a blind hole type of fixture.