J channels are most commonly used as a finishing touch along the edge of gables and around the trim of windows and doors.
Because of their hooked J shape on the end of the flange, most J channels can easily be installed by quickly cutting them down to the necessary shape and then snapping them in to place.
Many manufacturers design all-weather J channels to be sold in hardware stores. These can be coated with a variety of finishes to match or complement existing siding on a house. For example, some J channels are created with a brown, grainy finish giving the appearance of wood trim when installed.
The benefit of this is that installation of a J channel is cheaper and faster than using real wood, and it will not rot over time as it is exposed to moisture. J channels are used indoors as well to add a finishing touch around the interior of a window frame or other enclosure.
The manufacturing process for J channels is very simple, but it also depends on what materials are being used. If the manufacturing is done using plastic, a mold is employed to form the heated liquid into a J channel as it cools. These long pieces can then be cut down into shorter sections.
If sheet metal is used, a press in a fabrication plant will force the J channel into the correct shape, either by heating it or by using cold roll forming techniques to apply slow even pressure to the metal. This is a very quick production process, so manufacturers can quickly assemble J channels and ship them off to vendors to be resold or installed by contractors.
Some manufacturers will even offer to design and create custom J channels for unique applications or for building projects where the measurements are not typical of standard materials.