specific vehicle and its variants. Models and model kits Kits Models are usually assembled from commercial kits (for exceptions see below). Typically, a model kit consists of a set of parts, instructions for their assembly, and a small sheet of markings in decal form. Parts are produced by injection of liquid styrene plastic under very high pressure into complex steel molds. These molds are generally composed of two-halves that sandwich the parts; however, 'slide molds' may consist of many steel components to allow greater levels of detail to be incorporated into a single sprue. Once the plastic cools, it is removed from the mold. In the 1960s and 1970s, typical vehicle kits might contain 50 to 200 individual parts. Today it is common for a single vehicle kit to contain from 300 to 1200 parts. Each part must be carefully cut from the 'sprue' (the plastic channels that allow the plastic to flow into the mold and which hold the parts in place), cleaned of any flaws or mold marks, and then assembled. Instructions consist of paper booklets or sheets supplied with each kit. Usually, instructions show drawings of the parts. A recent trend has been the use of photographs rather than drawings, but these types of instructions have not proven popular and may be declining in use. For a kit with hundreds of parts, good instructions are vital. Flaws in instructions are not uncommon. Markings for the model usually are provided as decals. Several companies produce armor model kits, the most famous of which are Airfix, Dragon Models Limited, Tamiya, Trumpeter, Academy, Hobby Fan, Italeri, Revell-Germany/Monogram and AFV Club. The focus of many manufacturers of late has been to increase the accuracy of their kits and provide alternative types of material such as photo etch details and turned metal barrels. Models Completed models can be categorized generally into three classes: kits built 'out of the box', customized kits, and scratchbuilt models. "Out of the box" models Models built 'out of the box' are built according to kit instructions, using no materials except those provided in the kit itself. In the past, there was some tendency to view 'out of the box' builds as simpler or of a lower standard of detail than modified kits (see below). However, recent trends in which kits contain over 1,000 individual pieces including parts from plastic, etched brass, and aluminum have given new meaning