These hard rubber wheels measure 3" dia x 1" with a 5/16" ID and a hub that extends exactly one perfect smidgen, making them 1-3/16" wide at the axle. Outside surface is slightly (call it a micro-smidgen) convex.

Nice multipurpose wheel measures 4-7/8" dia x 1-1/4" with a gray plastic wheel and a hard rubber tire with straight-line treads. The 7/8” dia hub is flush on one side, and protrudes 3/8" long on the other (inside) with a 3/8” bore all the way through.

These black rubber-treaded wheels are as smooth as a baby’s bottom--if you’re talking about a rubber baby. Measure 8” x 29/32" wide with (8) plastic spokes. Bearings are 7/16” ID to take a 7/16” shaft, but they come separate and will need to be tapped into the center bore. Should make for a ride as smooth as a baby buggy.