THE wing spars designed for passenger jets at GKN's new aerospace works at Western Approach, near Bristol, are 27m long but must be accurate to within 0.3mm. Such tight tolerances are needed because many of the important bits of an aeroplane (the fuselage, landing gear, flaps and so on) bolt on to them. But what makes these wing structures special is that they are made solely of carbon-fibre composites, as strong as steel but far lighter, and so easier on fuel consumption.

Few of the 300-odd staff at the facility—opened in April by George Osborne, the chancellor of the exchequer—work on the two factory floors. In the first shed a robotic head layers carbon-fibre tape at prescribed angles, which determine the shape, strength and flexibility of the wing spars. The machine is sealed and air removed after each round of layering to increase the material's density. The structure is then cooked in a high-temperature oven for 10-12 hours. Once galvanised and tested, each piece is ready for fully automated assembly in the second shed. The finished spar is dismantled and sent by road to Airbus's facility in Broughton, en route to Toulouse in France.

“Only three or four firms in the world can do what we do,” says Marcus Bryson, head of GKN's aerospace division. Its expertise in new materials has made GKN a cornerstone of Britain's aerospace industry, said by the government to be the largest outside America and one of the shining hopes for future growth in manufacturing. Why, when so many widget-makers have gone to the wall or been bought up by foreigners, is GKN alive and kicking and British-owned after 253 years?

A firm might survive this long if age had given it authority with customers, as sometimes happens with newspapers; if its edge stems from an important natural resource, such as an oilfield; or if it is in an industry like banking where big incumbents are rarely allowed to fail. Manufacturers, by contrast, are often weighed down by their past—by pension debts and over-commitment to dud technology—or caught out by a more volatile business cycle. Such traps make GKN's longevity all the more remarkable.

The trick it has mastered is finding new businesses and markets to move into before its established ones run out of steam. “We have been very good at recognising that things don't last forever,” says Nigel Stein, GKN's chief executive since January.

The company owes its name to an early marriage between Welsh heavy industry and Midlands metal-bashing, brokered by Arthur Keen, a Victorian entrepreneur. In 1900 Keen's nuts-and-bolts company merged with the Dowlais iron company, founded in 1759 and managed from its early years by the Guest family. Shortly afterwards Keen bought Nettlefolds, which made screws and fasteners. In 1986 “Guest, Keen and Nettlefolds” became GKN.

The firm repeatedly leapt off one horse and on to another but the crucial jump came from the mid-1960s, when it was building up a business making the driveshafts that connect car engines to wheels. It bought Birfield, a British rival with better technology, and later extended its control over Uni-Cardan, a German-based maker of transmission gear for carmakers in continental Europe.

Such acquisitions kept GKN going when steelmaking and the low-tech bits of its business declined. It has thrived on the outsourcing by car firms of complex components and on the burgeoning demand for four-wheel-drive transmissions. GKN set up in China in the 1980s to serve Volkswagen, still one of its biggest clients. It now has 12 factories there, as well as ventures in Brazil and India. Globalisation has served GKN well. Its “driveline” division remains its leading business and produces parts used in two-fifths of the world's cars.

Two into one do go

The search for new business lines explains the recent emergence of GKN's aerospace division; a fledging barely a decade ago, it now accounts for a quarter of revenues and a third of profits. It is in large part the unanticipated by-product of an attempt to build a defence business through the purchase of Westland Helicopters in 1994. Westland was sold at a handsome profit a decade later to pay down GKN's pension debts. But by then the firm's sideline in lightweight composite aircraft parts had given GKN an entry into aerospace. A collaboration with Airbus on composites led to an order to design and build wing parts for the giant A380 jet, launched in 2005.

The aerospace venture might seem to sit awkwardly in a company whose mainstay is selling car parts but Mr Stein says there are “soft synergies” between the two divisions. Both make high-precision kit for a few global firms: it takes the same set of skills to serve and sustain the trust of such demanding customers. GKN has built up its aerospace business by capturing outsourcing contracts, just as it did in its driveline business. And some firms have begun to explore the use of carbon fibre in cars.

The A380 orders gave GKN a start in civil aerospace; a bigger milestone was the purchase in 2001 of Boeing's factory in St Louis, Missouri, which supplied parts for military aircraft. In 2009 GKN bought the Airbus wing factory at Filton, near Bristol.

The firm hopes the new factory at Western Approach, an offshoot of the Filton works, will help it grasp a big share of the world market for carbon-fibre wing spars. That market has seductive long-term prospects: as poor countries become rich, their citizens will travel more by air; the rich world's civilian aircraft fleet is ageing; and new aeroplanes made with lightweight materials are up to 40% more fuel-efficient than old ones. Airbus has over 550 orders for its new A350 XWB aircraft, with its all-composite wing spars made by GKN and a mainly British supply chain. Small wonder that the chancellor found £60m ($92m) in his most recent budget to fund an R&D centre for Britain's aerospace industry.

Sitting on their hands

The stockmarket, though, seems far from carried away by GKN's prospects. At £1.76 a share, the firm trades at eight times its 2011 earnings, scarcely a rich rating. GKN is still mainly thought to be a car-parts outfit with hard-bargaining customers that keep its profit margins a lean 7% (though aerospace margins are more generous at 11%). Investors have seen what a credit shock can do to the car industry and its suppliers. GKN's stock price fell below 50p in 2009, when the shortage of credit on reasonable terms led the firm to turn to the stockmarket for money to finance its growth. And the mess in the euro area poses a fresh threat to cyclical businesses such as GKN that fall hardest in a downturn.

But Mr Stein remains sanguine. GKN's global diversity will help mitigate any further trouble in Europe, he says. A firm that on the eve of the 1980s employed 69,000 people in its domestic market alone now has a worldwide staff of around 44,000, of whom about 5,800 are in Britain, mostly in aerospace. In this respect, GKN is a microcosm of modern British manufacturing: lighter and more efficient than its Victorian forebears; global, but with the promise of long-term growth at home.