Solid bicycle axles often use an uncommon thread pitch (26 tpi, IIRC, even on some metric axles), meaning wingnuts may not be as easy to find as you'd think. But there've been a bunch of different diameters and threadings used over the years, so it doesn't hurt to give it a shot. If Home Depot and Lowe's don't have something, other hardware stores often have better fastener selections.