 The use of single drivers gave several advantages.The weight of coupling rods was avoided and the second axle could be smaller and lightweight, as it only carried a small proportion of the weight.Rocket placed just over  tons of its  ton total weight onto its driving wheels, a higher axle load than "Sans Pareil", even though the 0-4-0 was heavier overall at 5 ton, and officially disqualified by being over the  ton limit.