Bicycle axis is the rotating component in the bottom bracket shell which connects the right and left cranks. Square hole axis, spline axis and integrated axis are the most popular in the mountain bicycle market.
Square hole axis is the most traditional one. It?s easily to be recognized from its two square ends. It has 4 contact surfaces which can make the crank bear the pressure much more evenly, and it has high intension. It has had been popular in the market for quite a long time.

Last century, SHIMANO produced a system of spline axis called OCTALINK(it?s also known as plum blossom). To resist SHIMANO?s technological monopoly, other manufacturers like RACEFACE,TRUVATIV,FSA released jointly another system of spline axis named ISIS. These systems can be telled directly from the quantity of the splines, OCTALINK has 8, while ISIS has 10. Compared with Square hole axis, spline axis has much more exquisite contact surface, and it can be combined better with the crank, and it?s not loose, and it has long axis dia., and it also has higher intension which enables it has much better power transmit ability. It?s taken the place of traditional square hole axis since it came to the world. Only several low end mountain bicycles still use Square hole axises.

Many manufacturers began to bring a new idea of the integrated axis not long after the spline axis, and tried to produce some whcih can be used in high end moutain bicycles. Integrated axis is a kind of systerm that separates the axis and its bearings and connects directly to one side of crank and moves the bearings out of the bottom bracket shell to two sides. This systerm reduces the quantity of parts, so as to cut the weight and improves the structural rigidity in the meanwhile, and it also reduces the burden of bearings and increases intension by broaden the space between bearings.

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