3-Piece Forged wheels can use many different methods of manufacturing. Centers can be cast in various methods or forged. The rim sections for 3 piece wheels are normally spun from disks of aluminum. Generally, spun rim sections offer the ability to custom-tailor wheels for special applications that would not be available otherwise, for example widebody applications. The rim sections are bolted to the center and normally a sealant is applied in or on the assembly area to seal the wheel. This type of 3-piece construction was originally developed for racing in the early 1970s and has been used on cars ever since. Three piece forged wheels are usually the most expensive wheel construction, mostly due to the assembly labor and components used. The wheels consist of three main pieces; the center, the outer barrel (lip), and the inner barrel. These three parts are held together with a series of perimeter bolts. Silicone RTV is used to seal between the two hoops.