Load-in and load-out of your subs has never been easier than with the JBL WK-4S subwoofer caster kit. Each of these metal casters bolts to the rear panel of your JBL subwoofer with the sub's pre-installed hardware, for easy-rolling transport that helps prevent injuries. Rear-panel placement accommodates the JBL subwoofer covers, too, guarding your sub against liquids and dust while in transit. Even with the ergonomically placed handles JBL subwoofers feature, many consider the WK-4S caster kit a must-have for safe, efficient transport and positioning of JBL subwoofer enclosures.