Potter & Brumfield W23-20 amp trip free 3/8″ bushing mounted circuit breaker.
This push-pull CB has 3/8-24 mounting & 8-32 wiring hardware included.
The mounting hardware consists of 2 hex nuts & lock washer.
The CB is about 0.680″ wide x 1.490″ tall & 2.6″ overall length.
The W23 CBs will protrude about 2.2″ behind the panel when mounted.
Remember you may need further room behind the panel for wiring.
See Potter & Brumfield W23-W31 Catalog for mechanical/electrical details.