Platform Caster Wheels with swivel. The wheel itself is made of plastic but the platform & hardware are made of steel. The platform is really perfectly shaped to bolt onto a 2 x 4 piece of wood.

Measurements:

• 4" diameter wheel
• 1 1/2" Wide Tread
• 3 7/8" ID Platform on top that is 4" long
• 3/8" Bolt in center of wheel
• 3/4" Raised sides of platform
• 3/8" Bolt holes in the platform sides