9/21/2013 11:14 AM
Edited Date/Time: 9/21/2013 11:23 AM

The spindle is what the cranks hold/clamp on to. It spins..
The splines are kinda like little teeth for the cranks to hold to. Cranks are also splined on the inside for that specific spindle. Some spindles have 48 (teeth) others less.. like 16 splines for example.
Spindle bolts screw into the spindle itself, after the cranks are installed. They're just bolts.. they keep your stuff tight.
Here is a pic of two different sized spindles. They're measured in circumference. 19mm would be the smaller (skinnier) compared to a heftier 22mm spindle.(19 and 22 are the most common sizes) When buying a new crank set, you have to take into consideration the size of your bottom bracket bearings. The bottom bracket is the part of your frame that holds the bearings.. which hold your spindle.. which hold your cranks.
So if you happen to buy a 22mm crank set then you would need bearings which are also 22mm to accommodate that 22mm spindle.
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