D. Zinc Cross Drilled Swivel Stem Caster

All wheels feature fully sealed bearings, permanently lubricated for a life of trouble-free service. High heat wheels are phenolic resin-molded, capable of withstanding temperatures from 50° to 300°F.
Polyurethane Wheels - Non marking and longer life than rubber.
Rubber Wheels - The traditional, economic and durable choice for years.
Solid Wheels - Made of either a polyurethane or rubber tread around a metal center. Requires greater effort to move than pneumatic wheels, but is also much less expensive.
Semi-Pneumatic Wheels - Made of rubber or polyurethane. The inner tube of air makes movement easier than a solid wheel. Wheel cannot be refilled, so replacement is necessary if punctured.
Full-Pneumatic Wheels - Just like a bicycle or car tire. Includes valve for inflating. Easily moves over most surfaces. Lasts longest and has the most durability, but is also more expensive.