Nearly 2,000 wooden shapes fill three warehouses at the Edgar Allen forging works in Bathgate, near Edinburgh. Each is worth around £15,000 to £20,000 and more are made as needs arise.
They are patterns, the starting point for casting a rail crossover, the X-shaped central section of a 'turnout', more usually known as railway points.
From these a 'negative' mould is made. Sand with a resin additive is packed around the wooden pattern which is then removed, leaving the cast ready for the steel pour.
The presence of so many patterns reflects the hundreds of different line layouts in the UK, with variations in angle, length and inclination of the crossovers.
Over its more than 100 year life, Edgar Allen has accumulated the blueprints for points across much of the network.
'The long history of the railways in the UK means that line routes follow contours and property boundaries more closely than in most countries, ' says Ronnie Davidson, production manager at the firm, which has been owned and run by Mowlem Rail for the past five years.
'In Europe and the US, where rail lines follow much straighter routes across country, there are a maximum of about 50 types. We export to both these markets too, and currently have about 30% of the US market.' Manganese steel, used for the crossovers, is a particularly difficult material.
The alloy, containing around 12% manganese, has a 'work hardening' property. The harder it is hit the harder it gets.
'It starts out at 200 Brinell (the unit of hardness) and rises to 450 in use, ' says Bob Laird, managing director at Bathgate.
That means it is difficult to cast and harder to finish.
Unsurprisingly, therefore, there are few makers worldwide.
Edgar Allen, with facilities in Bathgate and Sheffield, each employing around 120 people, is the only manufacturer in the UK, producing turnouts and rail junctions primarily for Network Rail's renewals programme.
Typically the rail design consultant will supply an overall layout and dimensions from which Edgar Allen's designers work up the detail, including rail sections, switch blades and crossings.
'We do everything down to the position of the bolts and joints.' Major projects include the multiple interchanges for the high speed Channel Tunnel Rail Link lines into St Pancras station and a heavy duty high speed line crossing at Newark, recently replaced. The Hong Kong airport line and metro projects have been notable exports, but projects are based throughout the world.
The exception is Germany, where a completely different rail engineering approach is used, with crossings made from bolted line sections.
Smaller layouts are made up in the works carpark before being disassembled and transported to site by truck. But new intermediate stainless steel fixing of the manganese steel to carbon steel extension rails has made some turnouts cumbersome and the firm is working on transportable workshops that can be set up on site. The former fishplate fixings were vulnerable to fatigue cracking.
Bathgate also sells crossovers to other interchange manufacturers, for example Mowlem rival Balfour Beatty.
Edgar Allen used to cast other items such as pump parts. But since take-over by Mowlem it has focused much more on rail. Not only is there a steady UK market, but the firm sees major export opportunities from the worldwide growth in rail, particularly in India, China and the USA.