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For anyone who loves the intricate world of threads or aspires to dive into it, a bicycle serves as a veritable treasure chest of different thread types. With its vast array of threads, the bicycle presents a fascinating study, especially when you consider that some of these threads are anything but ordinary—take, for example, the ones found on bicycle pedals. Overall, the range of bicycle thread types represents a blend of standards and sizes that you wouldn’t expect from any contemporary vehicle.
As it happens, the origins of this diversity can be traced back through history. The bicycle, a steadfast companion since its inception nearly 200 years ago, started out resembling the balance bikes children enjoy today. Despite its humble beginnings, the bicycle quickly became a staple mode of transportation. During the 19th and early 20th centuries, when motorization was still a distant dream, bicycles stood as essential modes of transport.
Consequently, many pioneering innovations in bicycle technology hail from this era, long before globalization and universal standards took hold. Each nation developed its own set of bicycle thread standards, some of which gained international acceptance while others did not. This patchwork of standards and measurements remains intact today, making it particularly intriguing for do-it-yourself enthusiasts who enjoy tinkering with their bikes.
Let’s delve into the various types of bicycle threads. The bicycle boasts its unique threading system, yet it lacks global uniformity. For instance, the British BSA thread follows an inch-based system, whereas the French thread adheres to the metric system. Interestingly, the Italian thread cleverly merges both systems. Except for the Italian thread, which features a 55° flank angle, all the threads mentioned earlier have a 60° flank angle. Given these similarities, confusion can arise, especially with the increasing prevalence of foreign-made bikes. Always double-check to avoid mistakes.
Additionally, Germany has its own specific bicycle thread, standardized as DIN 79012. Known as the FG thread, it’s relatively fine but doesn’t meet the criteria for a fine thread. Its dimensions are somewhat perplexing since they’re expressed in millimeters yet reference old inch measurements. Therefore, FG 2 does not correspond to a nominal diameter of 2 mm but rather 2.096 mm, with the pitch provided in threads per inch.
Beyond the FG thread, bicycles also feature valve threads and metric ISO threads. The valve thread, standardized under DIN 7756 and denoted by VG, includes the nominal size in millimeters, with the pitch specified in threads per inch. Like the other threads, it carries a 60° flank angle.
Finally, bicycles incorporate the familiar metric standard thread DIN 352 and the metric fine thread DIN 2182. The standard thread begins with the M prefix, followed by the nominal diameter, and has a 60° flank angle. The metric fine thread also exhibits a 60° flank angle but with a smaller pitch. Identified by MF, followed by the nominal size, it finds application in various components.
Now, let’s explore where these threads are located on bicycles. The FG thread, originally designed for high-stress components like axles, is predominantly used in solid axles, both front and rear. Some bottom bracket shells also utilize the FG thread. Spokes and nipples invariably employ this thread due to the immense forces they endure. Racing bikes often use FG 2, standard bikes FG 2.3, and cargo bikes FG 2.6. Pedals and cranks typically feature the FG 14.3 thread, with the left pedal’s thread being left-handed to prevent unscrewing during pedaling.
The valve thread, fortunately, is simpler. It exclusively appears on wheel valves, serving a critical role by protecting the valve from moisture and debris.
Lastly, the metric thread covers all bicycle parts not addressed by FG or VG. The standard M thread is prevalent in brakes, gears, and seats. The finer MF thread is more commonly found on chainrings, crank mounts, cable pulls, chainring lock nuts, and mounting points.
If ever in doubt, seek professional advice. Given the multitude of bicycle thread types, repairs or custom builds can prove challenging. Identifying the correct thread types may require consultation with an expert or the use of a thread gauge. BAER, a renowned thread tool manufacturer, offers both solutions. Visit their online store for thread cutting tools and more, or reach out to their customer service for guidance.
June 22, 2025