The PGSB-4A from ESSENTRA is a round, black, non-threaded plastic insert. It is an anti-vibration component commonly used in furniture, including chairs, sofas, and tables, to provide extra stability and reduce movement. The PGSB-4A features two internal threads and a rib around the outside that helps to grip the furniture pieces and hold them in place. It also helps to disperse any vibrations throughout the furniture, providing improved comfort levels and user experience.