What are B&W Phase Correction Plugs?

I have 802N speakers...what effect would the use of these aluminum B&W phase correction plugs (rather than the plastic plugs used now) have with my midrange drivers and will they fit this vintage of driver?

I was told by B&W that the new ones are graphite rather than the plastic with the original Nautilus speakers at about $30 a piece. The B&W rep thought they would not make an audible difference but may try them anyway.