Wheel axle spacers are made to be used when the hub of the wheelchair wheel is smaller than the fork width. Put spacers on both sides of the wheel.
Wheel Axle Spacers
You use these wheel axle spacers when the hub of the wheelchair wheel is smaller than the fork width. In order to keep your wheels centered when doing this you will need to use a spacer on each side of the wheel. This will keep your wheel centered inside the wheelchair fork.