Axis Wikipedia

Axis, is mounted on the frame for connection within five pass around the crank rotating parts. General sports car common square holes, splines, and one-piece three kinds.

A square hole axis 
Square hole axis is most common, because two are square, so easy to identify. It is based on the traditional axis of the pin-type improvements comes through. Pin type axis is carried out by single pin lock, because the contact surface is small and prone to loose and damage. Now only seen in quite old civilian car. Performance on the central axis of the square hole in that a one to four contact surfaces, the force is more uniform, higher strength and better power conduction, thus dominate the market for quite a long period of time. Each manufacturer has a square hole axis models.

2 splined bottom bracket 
The last century, SHIMANO launched a so-called OCTALINK splines (commonly known as “Plum”) bottom bracket standard, while other manufacturers (such as RACE FACE, TRUVATIV, FSA, etc.) in order to resist the technological monopoly SHIMANO then jointly launched the so-called ISIS axis formats. The difference between the two formats is that the appearance is 80 cents a spline (OCTALINK), and the other is 10 angle splines (ISIS); a tooth pattern and axial length smaller than the Dayton (OCTALINK), another relatively sharp tooth pattern the axial length of the pitch denser and larger (ISIS). Splined bottom bracket axis compared with the square hole, the contact surface more and more detailed, better able to bind to the crank, easy to loose, the greater axial diameter, high strength forces conducting good, so gradually replaced the square hole axis the original position.

3 one axis 
Splined bottom bracket has just launched a few years, various manufacturers have introduced the concept of one axis, and the production in its high-end series. The so-called one-piece, that is, the axis of the bearing axis separation, combined direct and crank side, and bearing positions within the five-way moved by both sides. This format has the advantage of reducing the number of parts to reduce the weight of the structure but increase the rigidity, the greater the spacing between the bearings, reducing the burden on the bearings, increases the strength. In fact, this technology very early in the BMX (BMX) were widely used, and rare.
In this case, Tell me what you will say: “? Asanas that do not is the best,” In fact, sometimes not all. For example, the square hole hollowed axis by axis will use titanium or even change the bearing forms to enhance their performance, especially splined bottom bracket. And one-axis performance also on other factors tooth disc, etc., so you can not generalize, to analyze specific issues. So you can choose the most suitable product.