These are nice rubber wheels / rollers for your robot / gizmo project.
They are a pliable, yet firm rubber with a nice "tack" to them.
The Inside diameter is 6mm (0.20 inch) but can easily bored to 0.25 inch with the nice plastic hub.
Inside Diameter: 6mm (0.20 inch)
Outside Diameter: 22.5mm (0.76 inch)
Length: 40mm (1.35 inch)
Item weight is 0.04 pound.