NPS plug with three quarter in vent plug

drum plug, drum bung, vented drum plug

2 inch drum plug w/ 3/4″ yellow vent plug
Item # SPP-C39-9AD 3/4″ Yellow vent plug
Item # RKCPPA5319143 2″ NPS Plug HD Diaphragm Blanked Out (DBO)- Fine Thread

This image shows the underside of a 2″ drum plug that has had a 3/4″ yellow vent plug threaded into it’s center reducer. Vent plugs feature relief holes covered by a microporous membrane.