Which Remington 870 mag extensions fit flush with the barrel?

[montesa]

I want to add a magazine extension to my 870.

From my research it seems that only the Remington factory extension fits flush with an 18.5" barrel.

Can anyone verfiy this?

I was considering a nordic components extension but it fits flush with an 18" barrel from what I understand.

 

[ProBusiness]

just wondering: why the concern if the mag ext fits flush with the barrel?

 

[montesa]

I prefer the way a flush fitting extension looks.