When did American automakers switch to metric bolts? – Jalopnik

The 1970s were a turbulent time for the American auto industry. Not long after the start of the decade, the dense fog of the Malaise era set in, giving us countless love-it-or-hate-it models, many of which featured an iconic Bustleback design. Emissions standards were implemented, leading to the widespread use of catalytic converters (which was definitely a good idea) and brutally low engine power. However, there was one bright spot that made life easier for professional mechanics and do-it-yourselfers alike: that was when American automakers started switching to metric bolts.

The key word here started because for years metric bolts have not completely replaced the standard, also known as Imperial, English or SAE fasteners. There is no shortage of discussion on this topic on popular Internet forums, but in terms of when America’s big three automakers first made their commitment, it would be the early 1970s. However, conversions were slow – to the point that some vehicles were fitted with both standard and metric fasteners.

Replacing standard with metric was not a cottage industry move. According to an article by the New York Times From December 1975 onwards it was General Motors that was the first to take the plunge. “When General Motors decided to switch to metric in 1973, letters announcing the switch were sent to its 47,000 suppliers,” Rita Reif wrote at the time. “Six months later, the manufacturer held a meeting for 600 nut and bolt suppliers to explain the threading system it had adopted. The mostly metric Chevette was the result.”

The Chevy Chevette is an excellent example. This platform and badge, coded internally by GM as the T-car, is sold in markets around the world, known as the Vauxhall Chevette in Europe and the Opel K180 in Argentina. But it wasn’t a direct import: GM brought the plans to the US, where they were reworked for American consumers in just 18 months. One of the hallmarks of the international DNA was the offering of two engines, a 1.4-liter and a 1.6-liter four-cylinder. While engine size is measured in liters today, cubic inches were the prevailing benchmark at the time of the Chevelle, making it unique in more ways than one.

Above all, the move to metrics was a move by the manufacturing industry designed to save money. The Times went on to report: “Moreover, metric opposition is crumbling as early predictions of astronomical conversion costs have been revised. Lower estimates have been reported by both industry giants that are already predominantly metric…”

Today, most of the world uses metric fasteners. However, as shown by a handy quiz from NapaMyanmar (written as Burma in the quiz) and Liberia keep the old-fashioned standard life.

There was no specific date indicating that all bolts would be metric. If Hot Rod Magazine In March 1985 it was noted: “Older engines and chassis may have a combination of both standard (English) and metric fasteners. Proper identification of these new fasteners is critical to replacing damaged parts with correct and safe new parts.”

Hot Rod Magazine also clarified that not only can American metric bolts differ from their European and Japanese counterparts, but also that “most American metric bolts and screws (as well as many nuts) have numbers embossed on their heads… they identify the tensile strength properties. Thus, a bolt marked ‘8.8’ has been heat treated to DIN Grade 8.8 strength properties.” Tensile strength between metric and standard bolts do not match. Interestingly, U.S. automakers only began moving to metric wiring standards in the early 2010s.

Today, metric is the unifying bolt size among United 50 automakers. The 1970s were the tipping point, and with its introduction a whole new level of knowledge became necessary if you were ever going to be able to compare standard and metric hardware sizes, tensile strengths, and so on.