JBL WK-4S Swivel Casters - Set of 4Load 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