The Tamiya Ball Caster from Tamiya's educational construction series is a small steel ball that rests on metal rollers inside a plastic housing. The caster can be assembled in two different ways, so that it has a total height of either 25mm or 35mm. The kit contains two complete ball casters and various types of mounting screws as well as spacers for small height adjustments.
Features:

Sold in pairs
Pivot and move in almost any direction
Adjustable height between 25 and 35mm

Specifications:
Height: Adjustable (25mm or 35mm)
Width: 28mm x 28mm