The HOLLOWTECH II bottom bracket system has made changing cranksets less complicated. After a brief introduction to this system, I discuss current Shimano MTB crankset options.
HOLLOWTECH II cranksets have the bottom bracket (BB) axle fused to the drive side crankarm. While the non drive side crankarm attaches to a splined region of the axle using pinch bolts. The advantage of this system is that the BB bearings are externally mounted to the frames BB shell. Consequently the BB axle can be a larger diameter, making it stiffer and lighter and replaceable sealed bearing cartridges can be used with some bottom brackets. I use the Hope bottom bracket to avoid the one fault of some HOLLOWTECH II bottom Brackets, premature bearing failure.
Previously other bottom bracket standards such as with Square taper and OCTALINK had separate axle. Consequently, these are called three-piece crankset. Changing your crankset often needed a different bottom bracket axle length to achieve the correct chainline. This process was normally accomplished with a trip to your local bike shop.