Guy,
All the responses are good, however if you use a 5-40 bolt, which is 1/8 diameter, for your axle, you can use a piece of 5/32 diameter brass tubing for a wheel bushing. The 5/32 brass tube has a 1/8 inside diameter, which is compatible with the 5-40 bolt.
The benefit of this set up is that when at the field and if having trouble with a wheel, you can borrow a wheel from just about anyone. Most wheels have a stock 1/8 diameter axle hole, allowing you to put it on the 5/40 bolt and not have it wobble. This is the way I do it, and it works well.
Good luck;
Larry