The four legs inside the screen are pre-welded to the base. The lid is then bolted to the legs at the factory. Now you just take it out of the box and it's ready to install. The Guardian Cap does double duty. First, it gives you a chimney cap with a screen, making it a great choice for relining jobs. Second, it makes a great replacement cap for solid-pack, class-A chimneys. The Guardian Cap attaches to both reline and solid-pack, class-A jobs by sliding inside with a tight friction fit. It is UL Listed for use with Home-Saver Flex relining pipe, and works great with Heat-Fab rigid stainless reline jobs, too.