overlap of one and half corrugations, and a vertical overlap of about , to provide for waterproofing. CGI is also a common construction material for industrial buildings throughout the world. Wrought iron CGI was gradually replaced by mild steel from around the 1890s, and iron CGI is no longer obtainable, but the common name has not been changed. Galvanised sheets with simple corrugations are also being gradually displaced by 55% Al-Zn coated steel or coil-painted sheets with complex profiles. CGI remains common. Corrugation today Today the corrugation process is carried out using the process of roll forming. This modern process is highly automated to achieve high productivity and low costs associated with labour. In the corrugation process sheet metal is pulled off huge rolls and through rolling dies that form the corrugation. After the sheet metal passes through the rollers it is automatically sheared off at a desired length. The traditional shape of corrugated material is the round wavy style, but different dies form a variety of shapes and sizes. Industrial buildings are often built with and covered by trapezoidal sheet metal. Many materials today undergo the corrugation process. The most common materials for corrugated iron are ferrous alloys (e.g. stainless steels), aluminium and copper. Regular ferrous alloys are the most common due to price and availability. Common sizes of corrugated material can range from a very thin 30 gauge () to a relatively thick 6 gauge (). Thicker or thinner gauges may also be produced. Other materials such as thermoplastic and fiberglass-reinforced plastic sheets are also produced with corrugations. Clear or translucent products can allow light to penetrate below. Pitch and depth The corrugations are described in terms of pitch (the distance between two crests) and depth (the height from the top of a crest to the bottom of a trough). It is important for the pitch and depth to be quite uniform, in order for the sheets to be easily stackable for transport, and to overlap neatly when joining two sheets. Pitches have ranged from 25 mm (1 inch) to 125 mm (5 inches). It was once common for CGI used for vertical walls to have a shorter pitch and depth than roofing CGI. This shorter pitched material was sometimes called "rippled" instead of "corrugated". However nowadays, nearly all CGI produced has the same pitch of 3 inches (76 mm). A design of corrugated galvanised steel sheets "Proster