Wheels are mounted to the axles of casters or trucks, carts, dollies, and other material-handling equipment to allow the equipment to roll. They make it easier to reposition large or bulky objects or move them from one place to another. Standard wheels may have a solid tread and core, or they may have a tread that's been mechanically joined to a core. Pneumatic, semipneumatic, and flat-free wheels have air-filled, foam-filled, or solid-rubber tires that absorb more shock and vibration and produce less noise than standard caster wheels. Track wheels have a molded V-groove or one or more flanges that fit into compatible tracks or rails. They provide optimum movement control and precise alignment when rolling heavy or large loads between two locations.