The journal of the axle A, is carried in a bearing or axle-box B, which is free to move vertically in the wide vertical slot G, formed in the frame and called generally " the horns," under the control of the spring.
The weight W 1 carried by the part of the frame supported by the wheel (whose diameter is D) is transmitted first to the pins P 1, P2, which are fixed to the frame, and then to the spring links L 1, L2, which are jointed at their respective ends to the spring S, the centre of which rests on the axle-box.
Assuming the wheels to roll along the rail without slipping, this couple will be equivalent to the couple formed by the equal opposite and parallel forces, F 1 acting in the direction shown, from the axle-box on to the frame, and F 1 =µ0, acting along the rail.
Engines of this class, with 78-inch driving wheels and the leading axle fitted with Webb's radial axle-box, for many years did excellent work on the London & North-Western railway.
