QO® (plug-on) and QOB® (bolt-on) one, two and three pole thermal magnetic circuit breakers provide overcurrent protection and switching on AC and DC systems. Plug-on QO® circuit breakers are for use in QO® load centers, NQ and NQOD panelboards, OEM mounting bases and Speed D™ switchboard distribution panels. Bolt-on QOB circuit breakers are for use in NQO and NQOD panelboards.