Adjustable Truglo Choke for Remington 870
If you don’t know what chokes are used for you can start with Shotgun Chokes Explained article.
So, if you can change chokes on your shotgun, you know that to change the barrel constriction you need to unscrew one choke and then screw in another one. But with adjustable choke, you don’t need to do this. Adjustable choke enables you to change constriction using just one choke, it is very handy and fast procedure.
Adjustable chokes are much more expensive than traditional chokes.