A Stub Axle is an axle fastened to an assembly that mounts on trailer's single side. It is not like a standard straight stub axle. Its an assembly part including spring and shock mounts. It moves freely as an essential part of suspension of the trailer. Even the rough road can be traversed with disturbing the load of trailer, if it uses a stub axle assembly. Just like an independent suspension on a sports car, the axle allows each tire and wheel assembly to move independently. It also improves cornering and braking characteristics, more likely on slippery roads. In many cases, the units are cast into the axle assembly, and the entire piece is considered as one single part, while in other cases, there are independent assemblies that fit into a trailer's receptacle and are a separate component. In any of the case, the axle has a single wheel and tire bolted to it. It is also used in a dual-wheel application.
As the Stub Axle is bolted into mounted assembly, or can be easily replaced if broken. The broken stub axle can be replaced by unbolting bolts and getting the broken stub out of the housing by sliding it. But in case of cast units, the entire unit with stub has to be replaced. It requires removing of shocks and springs.