Pololu Ball Caster with 1" Plastic BallPololu
This ball caster kit includes a black ABS housing, a 1" diameter plastic ball, three dowel pin rollers, two spacers (1/16" and 1/8" thick), and three #2 screw sets. The total height of the ball caster, 1.1", can be increased to about 1.3" using the included spacers. The three included #2 screws can be used to mount the ball caster to your chassis (the distance between the screw holes is 0.69").
Note that our ball casters are designed for small robots; they are not intended to bear more than a few pounds. With more weight than this, friction between the ball and the housing will probably keep it from rolling well.