The bicycle industry is well known for it’s lack of “standards” and hubs and bottom brackets seem to be the worst offenders! Here is everything you wanted to know about hub standards but were too afraid to ask! The more common types are highlighted in green.
Some hub “standards” use the outside of the hub’s endcap to locate in the frame or fork making installing the thru-axle much easier. For these types of “standards” the outside diameter of the endcap therefore becomes a critical dimension.
QR: Quick Release
Quick release hubs are held into the frame or fork with a 5mm quick release skewer which goes through the hub.
There are two key aspects to a thru-axle hub:
- Thru-axle hubs have a large diameter axle which threads into the frame or fork.
- The hub’s endcaps rest on a specially designed shelf inside the frame or fork. This makes installing the wheel easier.
Thru-bolts look very similar to Thru-axles at first glance, however a thru-bolt does NOT thread into the frame or fork and instead relies on it’s own included nut, and the hub’s endcaps do NOT rest inside the frame or fork. Thru-bolts are uncommon on modern bikes and have generally been replaced with thru-axles.
Thru-bolt front hubs tend to have a 9mm shaft diameter. Thru-bolt rear hubs tend to have either a 10mm or 12mm shaft diameter.
Here’s an example of a front thru-bolt with it’s nut.