or Overall Height
Caster height is the combined measurement of the wheel itself and the frame it is mounted in. Plate casters are measured from the point where the wheel touches the ground to the surface of the plate.
Stem casters should be measured from the point where the wheel touches the ground to the base of the stem.
Swivel lead is the distance between the vertical centerlines of the kingpin and the axle of a swivel caster.
Tread width is also called wheel width. The face is measured without a load on the wheel. Wheel diameter is usually the main measurement for a caster; for example a 6″ caster has a 6″ diameter wheel.