Is the distance from outside of hub mounting flange to outside of hub mounting flange, measured one-half way between top and bottom of hub. The hub face is also know as the mounting surface where the wheel studs are located.
Is the distance from tire centerline to tire centerline, measured one-half way between top and bottom of tire. A more precise measurment would be to measure the distance from one hub face to another.
Is the distance from centerline of spindle to bottom of the main axle tube.
NOTE: In straight axles, you measure from the spindle centerline and axle main beam centerline. Therefore this is no drop.
Is the distance between center of one spring to the center of the other.
Is the distance from center of spring to center of tire. Axle load rating decreases as overhang increases.
Spring Center Pads:
Are locating or centering pads that can be welded or left loose and are meant for the leaf springs to mount onto. Springs pads can be located at the top or bottom of the axle main beam. DO NOT drill holes in beam in lieu of using spring pads. This would set up stress concentration points, which will weaken the axle beam and allow water to enter the beam.
Hub Bolt Circle Nomenclature:
example: 5 on 4 1/2" means 5 lug bolts or studs on a 4 1/2" diameter circle. Other patterns are defined in the same manner.