An extension ladder having a base section having a first box shaped base rail having a base side and a groove extending along the side. The extension ladder has a fly section having a first box shaped fly rail, and a follower bracket attached to the first box shaped fly rail and extending outward toward the first box shaped base rail. The groove is sized to engage the follower bracket which constrains the fly section to have limited motion relative to the base section and a left to right and front to rear directions while permitting the fly section to slide freely relative to the base section when the fly section is extended. A method for using an extension ladder. A method for producing an extension ladder.