3" vs 4" Casters
The 3" caster (above) has a solid black phenolic wheel. A single row of heavy-duty ball bearings is partially enclosed next to the mounting plate, allowing 360 degree swivel movement.
The 4" caster has a blue wheel welded to an inner core. At the center of the wheel is a built-in ball bearing sleeve that helps increase the load-bearing capacity. There's also a double row of full swivel 360 degree ball bearings sealed inside the black dust cover next to the mounting plate. Double ball bearings act like a heat sink on an amp, allowing for a much smoother swivel action, and longer life for the entire caster.
The 4" caster is also available with an extremely heavy-duty "toe" brake that's built-in as part of the caster assembly. This front brake is much stronger than other "side" type brakes, which protrude from the outside and quickly become bent and non-useable.