Bicycle thread types: spokes, bearings and valves
For those passionate about threads and those eager to become so, a bicycle, with its myriad of thread types, is a true treasure trove. Bicycles not only have an abundant variety of threads, but some are particularly fascinating, like the threads on bicycle pedals. In total, the range of bicycle thread types is a medley of standards and sizes one would not expect from any modern vehicle.
As is often the case, the reasons for this can be traced back in history. The bicycle, as a faithful companion, has been around for roughly 200 years. Granted, early models resembled the balance bikes kids ride today, but it marked the beginning of the bicycle's unstoppable rise. Particularly in the 19th and early 20th century, when motorization was still a dream, bicycles established themselves as indispensable means of transport.
Thus, many groundbreaking bicycle technology innovations date back to this era—a time before globalization and global standards. Consequently, each country developed its own standards for bicycle threads; some were adopted elsewhere, some were not. This patchwork of standards and measurements has been preserved to this day, making it particularly interesting for DIY enthusiasts who like to get hands-on with their bikes.
Bicycle Thread Types: The Bicycle Thread
The bicycle has its unique threading standard. But due to its historical evolution, it isn't globally uniform. For instance, the British BSA thread is an inch-thread, the French thread is metric, and the Italian thread ingeniously combines both. Apart from the Italian thread with its 55° flank angle, all the threads mentioned have a 60° flank angle. The similarities among bicycle thread types often lead to mix-ups, especially now that foreign-made bikes are common in stores. So, it always pays to double-check.
Of course, there's also a German bicycle-specific thread, standardized as DIN 79012. The German bicycle thread FG is relatively fine but doesn't qualify as a fine thread. The dimensions can be tricky, given that they're expressed in millimeters but refer to old inch measurements. Hence, FG 2 doesn't have a nominal diameter of 2 mm, but 2.096 mm. The pitch is directly given in threads per inch.
Bicycle Thread Types: Valve Threads and Metric ISO Threads
Apart from the FG thread specifically intended for bicycles, we also find other thread types on bikes: the valve thread and the metric ISO thread.
The valve thread, standardized under DIN 7756, is denoted by VG. It's followed by the nominal size in millimeters, and the pitch is given in threads per inch. This bicycle thread type has a 60° flank angle.
Finally, bicycles also incorporate the familiar metric standard thread DIN 352 and the metric fine thread DIN 2182. The standard thread is identified by the M prefix, followed by the nominal diameter, and has a 60° flank angle. The metric fine thread also has a 60° flank angle but with a smaller pitch. It's denoted by MF, followed by the nominal size.
A Glance at Where Threads are Located on Bicycles
The realm of bicycle threads is intricate. Let's try to demystify it.
Starting with the FG bicycle thread, this type was primarily designed for components exposed to high stresses, like axles. However, only solid axles, both front and rear, employ this thread type. Some bottom bracket shells also use the FG thread. Clearly, however, spokes and nipples always have this thread due to the high forces they undergo. For racing bikes, FG 2 is used, FG 2.3 for standard bikes, and FG 2.6 for cargo bikes. Pedals and cranks typically employ the FG 14.3 thread. Notably, the direction of the pedal thread on the left pedal is left-handed, preventing pedals from unscrewing while pedaling.
The valve thread is thankfully more straightforward. Exclusively, it's found on wheel valves. These threads are crucial as the valve cap protects the valve from moisture and dirt.
Finally, the metric thread is essentially used for all bicycle parts not covered by FG or VG. The standard M thread is found in brakes, gears, and seats. The finer MF thread is more common, found on chainrings, crank mounting, cable pull, chainring lock nut, and mounting.
When in Doubt, Consult an Expert
Due to the plethora of bicycle thread types, repairs or custom builds can be quite challenging. Especially identifying the right bicycle thread types can be tricky. In such cases, either consult an expert or use a thread gauge. You can find both at BAER, the thread tool manufacturer! Explore our online shop for thread cutting tools & more, or contact our customer service with any questions.