The document discusses three types of rear axle casings: 1) Split type which has two halves bolted together and requires removing the entire rear axle for repairs; 2) Banjo or separate carrier type which has a one-piece casing that carries the differential unit and allows removing half shafts for repairs; and 3) Salisbury or integral carrier type which is like the banjo type but has permanent housing tubes welded to the differential housing, making it the most widely used type today.